Since the removal of President Viktor Yanukovich through deadly anti-government protests, Ukraine has called for fresh presidential elections on May 25.
The move was countered by the Crimea administration that voted overwhelmingly to join Russia in a referendum deemed illegitimate by the US and EU, but welcomed by Russia.
As the government in Kiev continues to emphasise the need for a united Ukraine, and world leaders strive to avoid military conflict, here is a timeline of some of the events that have led to the current situation.
Nov 21: Yanukovich announces abandonment of a trade agreement with the EU, seeking closer ties with Moscow.
Nov 30: Public support grows for pro-EU anti-government protesters as images of them bloodied by police crackdown spread online and in the media.
Dec 1: About 300,000 people protest in Kiev's Independence Square. The City Hall is seized by activists.
Dec 17: Russian President Vladimir Putin announces plans to buy $15bn in Ukrainian government bonds and a cut in cost of Russia's natural gas for Ukraine.
Jan 16 : Anti-protest laws are passed and quickly condemned as "draconian".
Jan 22: Two protesters die after being hit with live ammunition. A third dies following a fall during confrontation with police.
Jan 28: Mykola Azarov resigns as Ukraine's prime minister and the parliament repeals anti-protest laws that caused the demonstrations to escalate in the first place.
Jan 29: A bill is passed, promising amnesty for arrested protesters if seized government buildings are relinquished.
Jan 31: Opposition activist Dmytro Bulatov found outside Kiev after being imprisoned and tortured for eight days, apparently at the hands of a pro-Russian group.
Feb 16: Opposition activists end occupation of Kiev City Hall. In exchange 234 jailed protesters are released.
Feb 18: More street clashes leave at least 18 dead and around a hundred injured. Violence begins when protesters attack police lines after the parliament stalls in passing constitutional reform to limit presidential powers. Protesters take back government buildings.
Feb 20: Kiev sees its worst day of violence for almost 70 years. At least 88 people are killed in 48 hours. Footage shows government snipers shooting at protesters from rooftops.
Protest leaders, the political opposition and Yanukovich agree to form a new government and hold early elections. Yanukovich's powers are slashed. The parliament votes to free Yulia Tymoshenko, the former prime minister, from prison. Yanukovich flees Kiev after protesters take control of the capital.
Feb 22: Ukraine politicians vote to remove Yanukovich. Tymoshenko is freed from prison and speaks to those gathered in Kiev. May 25 is set for fresh presidential elections.
Feb 23: Ukraine's parliament assigns presidential powers to its new speaker, Oleksandr Turchinov, an ally of Tymoshenko. Pro-Russian protesters rally in Crimea against the new Kiev administration.
Feb 24: Ukraine's interim government draws up a warrant for Yanukovich's arrest.
Feb 25: Pro-Russian Aleksey Chaly is appointed Sevastopol’s de facto mayor as rallies in Crimea continue.
Feb 26: Crimean Tartars supporting the new Kiev administration clash with pro-Russia protesters in the region.
Feb 27: Pro-Kremlin armed men seize government buildings in Crimea. Ukraine government vows to prevent a country break-up as Crimean parliament set May 25 as the date for referendum on region’s status. Yanukovich is granted refuge in Russia.
Feb 28: Armed men in unmarked combat fatigues seize Simferopol international airport and a military airfield in Sevestopol. UN Security Council holds an emergency closed-door session to discuss the situation in Crimea.
Moscow says military movements in Crimea are in line with previous agreements to protect its fleet position in the Black Sea. Yanukovich makes his first public appearance, in southern Russia.
March 1: Russian upper house of the parliament approves a request by Putin to use military power in Ukraine.
March 2: A convoy of hundreds of Russian troops heads towards the regional capital of Crimea. Arseny Yatsenyuk, Ukraine's new prime minister, accuses Russia of declaring war on his country.
There can be one assessment of what happened in Kiev and Ukraine as a whole. This was an anti-constitutional takeover and armed seizure of power.
March 3: Russia's Black Sea Fleet tells Ukrainian navy in Sevastopol in Crimea to surrender or face a military assault.
March 4 : In his first public reaction to the crisis in Ukraine, Putin says his country reserves the right to use all means to protect its citizens in eastern Ukraine. Russian forces fire warning shots on unarmed Ukrainian soldiers marching towards an airbase in Sevastopol.
March 6: Crimea's parliament votes unanimously in favour of joining Russia. Hours later, the city council of Sevastopol in Crimea announces joining Russia immediately.
March 11: The EU proposes a package of trade liberalisation measures to support Ukraine's economy. Crimean regional parliament adopts a "declaration of independence".
March 12: Obama meets with Yatsenyuk at the White House in a show of support for the new Ukrainian government and declares the US would "completely reject" the Crimea referendum.
March 13: Ukraine's parliament votes to create a 60,000-strong National Guard to defend the country.
March 15: UN Security Council members vote overwhelmingly in support of a draft resolution condemning an upcoming referendum on the future of Crimea as illegal. Russia vetoed the action and China abstained.
March 16: Crimea's referendum goes ahead, with official results stating that at least 95 percent of voters support union with Russia.
March 17: The US and Europe put asset freezes and visa bans on individuals involved in the Crimean breakaway.
March 18: Putin signs treaty absorbing Crimea into Russia, the first time the Kremlin expands the country's borders since World War II. Kiev says the conflict has reached a "military stage" after a Ukrainian soldier was shot and killed by gunmen who stormed a military base in Simferopol, the first such death in the region since pro-Russian forces took over in late February.
| Pro-Russian activists, apparently Crimean self-defence forces, overtake Sevastopol base without using violence [Al Jazeera]
March 19: Pro-Russian activists, apparently Crimean self-defence forces, overtake Sevastopol base without using violence.
March 20: EU leaders condemn Russia's annexation of Crimea. EU and US extend the list of individuals targeted for sanctions.
March 21: Russia backs off from tit-for-tat sanctions after US targets Putin's inner circle and EU adds 12 names to sanctions list. Ukraine says it will never accept loss of Crimea while Moscow signs a bill to formally annex the peninsula.
March 22: Soldiers take control of Ukrainian airbase in Belbek, as Novofedorovka naval base is seized by pro-Russian activists. Crimea celebrates joining Russia.
March 24: Leaders of the Group of Seven nations, meeting without Russia, agree to hold their own summit this year instead of attending a planned G8 meeting and to suspend their participation in the G8 until Russia changes course.
March 25: Oleksandr Turchynov, Ukraine's acting president, orders troops to withdraw from Crimea after Russia seized and annexed the peninsula.
March 27: UN General Assembly approves a resolution declaring Russian annexation of Ukraine's Crimea illegal.
March 29: Ukraine's presidential race begins with former Prime Minister Yulia Tymoshenko and billionaire confectionery tycoon Petro Poroshenko registering as hopefuls. Former heavyweight champion Vitali Klitschko pulls out of the race, giving his backing to Poroshenko and urging Tymoshenko to do the same.
March 31: Russian troops partly withdraw from Ukrainian border in the south region of Rostov in Russia, following talks between Russia's foreign minister and his US counterpart. Meanwhile, Russia's Prime Minister Dmitry Medvedev visits Crimea, promising funds and pay rises.
April 1: NATO announces it is suspending "all practical civilian and military co-operation" with Russia.
| Pro-Russian activists seize control of government buildings in three Ukrainian cities [EPA]
April 2: Ukraine's ousted president admits he was "wrong" in inviting Russian troops into Crimea and vows to try to persuade Moscow to return the peninsula.
April 6: Pro-Russian activists seize control of government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence. Ukraine authorities regain control of Kharkiv buildings on April 8 after launching an "anti-terror operation".
April 11: Ukraine's interim prime minister offers to give more powers to the eastern regions, as pro-Russia separatists continue to occupy buildings in Donetsk and Luhansk.
April 12: Pro-Russian gunmen take over the police station and security services building in the town of Slovyansk, 60 kilometres from Donetsk where pro-Russian rebels take over the police headquarters. The separatists also seize a police HQ in Kramatorsk.
April 13: Ukrainian special forces fail to dislodge pro-Russian gunmen in Slovyansk. One Ukrainian officer and one pro-Russian activist are killed in the operation. Meanwhile, the separatists seize the city council buildings in Mariupol and in Khartsyzsk.
April 14: Putin and Obama confront each other during telephone talks. EU foreign ministers agree to expand the list of those hit with sanctions for their role in the Ukraine crisis.
April 15: Putin declares that Ukraine is on the brink of civil war. Politicians in Moldova's Transdniestr region call on Moscow and the UN to recognise its independence.
April 16: Ukrainian troops turn back from Slovyansk while a pro-Russian group seizes the town hall in Donetsk.
April 17: Ukrainian troops repel an overnight attack in Mariupol, killing three assailants. Around 200 people then demonstrate in the town against Kiev. Putin acknowledges that Russian forces were deployed in Crimea during the March referendum on joining Russia, but says he hopes not to have to use his "right" to send Russian troops into Ukraine. Lavrov announces in Geneva a deal has been reached with Ukraine, the US and the EU to "de-escalate" tensions in Ukraine.
April 18: Pro-Russian groups say they will not be moved from occupied buildings until the government in Kiev, which they see as illegitimate, is also removed. Russia condemns talks of more sanctions. Ukraine's interim government pledges broad independent governance and says the Russian language will be given a "special status" in the country.
April 20: A deadly gunfight in an eastern Ukrainian town shatters a fragile Easter truce, with Russia declaring it is "outraged" at the return to violence in the crisis-hit former Soviet republic.
April 21: Protesters in Luhansk pledge to hold their own local referendum on autonomy on May 11.
April 22: In Kiev, US Vice President Joe Biden says Russia faces "isolation". Washington orders 600 soldiers to Poland and the ex-Soviet Baltic states. Ukraine orders a military operation against pro-Kremlin separatists to resume.
April 23: Russia says it will respond if its interests are attacked in Ukraine.
April 24: Ukraine's military launches an assault on Slovyansk. Up to five rebels are killed, according to Kiev. Special forces seize back control of the town hall in the port city of Mariupol. Putin says deployment of military in east Ukraine by the Kiev authorities is a crime that will "have consequences. The Russian army starts new exercises at the border with Ukraine.
April 25: Ukrainian Prime Minister Arseniy Yatsenyuk accuses Moscow of seeking to trigger a "third world war". The Ukrainian military launches a offensive for a second day to besiege Slovyansk while rebels vow: "We will not surrender the town." Western powers led by US President Barack Obama warn that Russia faces fresh sanctions. They stress that a presidential poll scheduled for May 25 is "essential" to stabilise the country. Seven OSCE military observers are detained in Slovyansk .
April 26: Yatsenyuk shortens a Vatican trip, saying Russian warplanes violated Ukraine's airspace. Russia denies the claim.
April 28: The West imposes new sanctions on Moscow. Russia vows "painful" response. NATO says no sign of a Russia troop pullback claimed by Moscow. Russia assures US it will not invade Ukraine.
April 29: Russia warns sanctions could harm Western interests in Russia's lucrative energy sector, and denies it has troops in eastern Ukraine.
April 30: Kiev places its armed forces on "combat alert" against a possible Russian invasion, and admits police are "helpless" to stop rebels over-running eastern towns. The IMF approves $17bn aid package for the beleaguered Ukrainian economy.
May 1: About 300 pro-Russian fighters seize the prosecutor's office in Donetsk. Conscription is reintroduced for all Ukrainian men aged 18-25.
May 2: The bloodiest day since the new government came to power. At least 10 die in fresh army assault on Slovyansk. In the southern city of Odessa, 42 die when clashes between pro-Russian fighters and pro-Ukraine supporters culminate in a massive blaze. Russia declares the Geneva peace plan dead and calls an emergency UN Security Council meeting. US President Barack Obama warns of further sanctions if Moscow's actions prevent a planned May 25 presidential election in Ukraine.
May 3: Slovyansk rebels free OSCE inspectors after a Kremlin envoy intervenes. Fierce gunfights rage around Slovyansk and nearby towns as the military seeks to retake control.
May 4: Kiev vows to expand "anti-terrorism" operations. Yatsenyuk launches a probe into Odessa deaths.
May 5: A fresh assault begins on Slovyansk. The interior minister says more than 30 rebels are killed. Four servicemen are also killed. Russia warns Europe's peace is at risk. UN chief Ban Ki-moon offers to mediate personally as the West launches new diplomatic push.
May 6: Russia rejects a German-led move for a new peace meeting. Germany says Ukraine is on the verge of war.
May 7: In a surprise announcement, Putin calls for rebel independence referendums to be pushed back and endorses Ukraine's planned presidential election. He says Russian troops pulled back from border. The new overall toll from Ukrainian military operations stands at 14 servicemen dead.
May 8: Rebels vow to press on with referendums despite Putin's call. Russia conducts military exercises, test-fires several missiles, and says nuclear capabilities are on "constant combat alert." NATO says there is no sign of a Russian troop pull-back.
May 9: Putin flies to annexed Crimea after overseeing a display of military might in the Red Square where he paid tribute to Russia's "all-conquering patriotic force." Clashes break out in Mariupol that the interior minister says leave 21 dead.
May 10: France and Germany threaten to step up sanctions against Russia if the May 25 election is disrupted and urge Kiev to cease "offensive" operations before the vote.
May 11: "Referendums" are held in the provinces of Luhansk and Donetsk. Fighting is reported around Slovyansk as rebels try to retake TV tower.
May 12 : Pro-Russia activists declare resounding victory in a twin referendum on sovereignty for eastern Ukraine. The provinces of Donetsk and Luhansk voted on Sunday to secede from Ukraine. Russian gas giant Gazprom gives Ukraine until June 3 to pay $1.6bn for natural gas. The EU ramps up sanctions on Moscow.
May 13: Seven Ukrainian soldiers killed in rebel ambush in the deadliest single loss of life for the military since the start of the uprising.
May 14: Ukraine hosts "national unity" talks based on an OSCE roadmap but rebels are not invited.
May 16: A report from a UN monitoring mission describes an "alarming deterioration" of human rights in the country's east over the past two months.
May 17: A second round of "unity dialogues" takes place in Kharkiv.
May 19: Putin orders troop withdrawals from the Ukraine border following the "completion of spring military training programmes." Putin also appeals for an end to military operations and violence by the Ukrainian government.
May 21: US Vice President Joe Biden says the US must be "resolute" in imposing costs on Russia for its actions in Ukraine.
May 22: At least 14 people, thought to be Ukraine military personnel, are killed and more wounded after clashes with pro-Russia groups in Donetsk.
May 23: During an economic forum in St Petersburg, Putin says Russia will respect the results of Ukraine's upcoming election, but remains critical of procedures surrounding the vote, saying those in the country's south and east will not be represented.
May 23: Overnight clashes in Luhansk kill at least 32 and injure 44, with the majority of the casualties coming from the pro-Russia side.
May 25: Petro Poroshenko wins the Ukrainian presidential runoff, but reports indicate that access to voting was blocked or heavily impeded in many rebel-held areas of eastern Ukraine.
May 26: The Ukrainian military launches an offensive against armed groups in control of the Sergei Prokofiev International Airport in Donetsk, managing to take back at least part of the airport.
May 27: The Ukrainian military re-takes the airport in a two-day fight that claimed dozens of lives.
May 28: Pro-Russia rebels shoot down a Ukrainian transport helicopter, killing at least 12 people.
May 31: Denis Pushilin, a pro-Russian leader, says six more people were killed in the aftermath of the battle for Donetsk Airport.
June 2: About 500 pro-Russia separatists attack a Ukrainian border guard HQ in Luhansk. Five of the rebels were killed, while at least seven border guards were injured.
June 5: In a joint press conference, Obama and Cameron threaten to impose further sanctions if Putin does not stop Russia's actions in Ukraine.
June 7: Poroshenko is sworn in as Ukraine's president, calling on pro-Russian separatists to lay down arms and end the fighting. On the same day, Biden announces $48m in US assistance to Ukraine.
June 9: According to a statement by Ukraine's foreign ministry, Russia and Ukraine reached a "mutual understanding" after two days of talks regarding a "de-escalation of tensions."
The death of the Russian journalist near Lugansk has shown in its entirety the criminal nature of the forces that launched the military operation in the country’s east.
June 10: Poroshenko orders humanitarian corridors be created as fighting continues in eastern Ukraine. Meanwhile, clashes in Kramatorsk, Slovyansk and Luhansk leave about 40 people dead.
June 11: The Ukrainian government rejects a gas deal from Russia that would have included a discount of $100 per thousand cubic meters. On the same day, Ukraine's ministry of health says at least 270 people have died in eastern Ukraine since the Ukraine since operations against the pro-Russian separatists began in spring.
June 14: Russian separatists shoot down a Ukrainian military transport plane over Lugansk. All 49 people on board were killed, including 40 paratroopers. This sparked violent protests outside Russia's embassy in Kiev.
June 16: Russia halts gas deliveries to Ukraine, despite an offer from Ukrainian and European negotiators for an interim agreement. Gazprom announces Ukraine will only receive gas it pays for in advance.
June 17: A gas pipeline explodes on the Ukrainian border. Russia State television announces the death of journalist Igor Kornelyuk.
June 18: Poroshenko announces a temporary unilateral ceasefire, saying that all rebels who lay down their arms and have not committed "grave crimes" will be given amnesty, an offer met with scorn by many rebel groups.
June 19: NATO says it has evidence of a renewed Russian military build up along the border with Ukraine. Pro-Russian separatists demonstrate their rejection of the call for a ceasefire, prompting violence near the city of Krasny Liman.
June 20: Poroshenko announces a week-long ceasefire, saying Ukraine's forces will not fire unless fired upon.
June 22: Putin makes a public announcement supporting Poroshenko's plans for a ceasefire, calling for a "substantial and detailed" dialogue between Ukraine and the pro-Russian groups.
June 23: Pro-Russian groups agree to Poroshenko's ceasefire.
June 24: Putin's spokesman, Dmitry Peskov tells reporters Putin has asked the upper house to rescind its March 1 resolution allowing the deployment of armed forces in Ukraine, saying the decision was based on the beginning of three party talks in Donetsk. In a violation of the ceasefire, a Ukrainian transport helicopter was shot down.
June 27: Poroshenko signs an EU association agreement, eight months after protests over the abandonment of the agreement began.
July 1: Poroshenko ends a tentative ceasefire and launches military operations against pro-Russia rebels, saying "we will attack and liberate our land." The week-long ceasefire failed to produce any permanent resolutions.
July 3: Colonel-General Valery Heletey announced as Ukraine's new minister of defence.
July 4: Ukraine's government says the army has cleared 17 villages in the country's east of pro-Russia rebels, saying it now controls 23 of the 36 regions in Donetsk and Luhansk.
July 5: Ukraine's army recaptures Slovyansk, formerly a major rebel base. A simultaneous operation in Kramatorsk also forced the rebels out of the town.
July 7: Three bridges spanning motorways leading to Donetsk are destroyed, with both sides accusing the other for the action.
July 8: Ukraine rules out a unilateral ceasefire in a statement posted on the defence ministry's website.
July 11: About 30 Ukrainian soldiers are killed in a missile strike on Zelenopillya, a village near the border with Russia.
July 13: Russia accuses Kiev with killing a Russian civilian in an artillery attack, promising "irreversible consequences." Ukraine denies the charges.
July 14: The Ukrainian government reports the downing of a transport plane carrying food and water. The plane was reportedly flying at a height that was out of the range of rebel MANPAD systems.
July 15: An airstrike in the Ukrainian town of Snizhne kills 11 people. Ukraine says the strike was carried out by "unknown aircraft." Security council spokesman Andrei Lysenko calls the attack "a cynical and bloody provocation in order to discredit the Ukrainian military."
July 16: Obama announces a new set of unilateral sanctions targeting at least eight state-owned defence firms.
| MH17 shot down over eastern Ukraine
July 17: Malaysian Airlines flight MH17 is shot down of eastern Ukraine, killing all 298 people on board. An adviser to Ukraine's interior ministry states the plane was hot by a missile from a Buk surface-to-air launcher.
July 18: Obama confirms that initial assessments suggest MH17 was shot down by a BUK-M1 surface-to-air missile shot from territory controlled by pro-Russia rebels.
July 19: Kiev accuses rebel forces of tampering with evidence at the crash site, saying the armed groups were moving bodies and destroying evidence. Other reports indicate the OSCE monitoring group sent to the site was only granted limited access.
July 20: Several EU leaders threaten to impose further sanctions on Russia if the Kremlin does not pressure rebels thought to have shot down the MH17 passenger plane to grant more access to the crash site.
July 21: Fighting breaks out in Donetsk as Ukrainian forces try to regain control of the city. Pro-Russian groups hand over MH17's black boxes. Meanwhile, the first bodies of the victims are transported from the site.
July 22: The victim's bodies arrive in Kharkiv, Ukraine, to begin the journey home. Dutch experts say 200 of the 298 victims have arrived in the city, contradicting Ukrainian reports saying all the bodies were accounted for.
July 23: US intelligence officials say they believe the plane was shot down by pro-Russian separatists "by mistake."
July 24: The Us accuses Russia of firing artillery across the border into Ukraine, but does not share its evidence. A Pentagon spokesman describes it as a "military escalation." on the same day, the coalition government in Ukraine collapses, and Prime Minister Arseniy Yatsenyuk resigns following the withdrawal of the Svoboda and UDAR parties.
July 25: The EU agrees to an initial plan to increase economic sanctions in Russia. The deal would spread evenly the economic stresses caused to the EU nations involved.
July 26: The Ukrainian military advances on the city of Donetsk, relaunching an offensive to retake the region from the rebels.
July 27: A series of photographs released by the Office of the Director of National Intelligence apparently show Russian Artillery attacking the Ukrainian army.
July 28: International investigators trying to reach the MH17 crash site are forced to turn back because of intense clashes in the area.
July 29: The EU agrees to widen sanctions being imposed on Russia which would include and arms embargo. Meanwhile, the US accuses Russia of violating a 1987 nuclear arms deal, the Intermediate Range Nuclear Forces Treaty. Washington says Russia tested a cruise missile that violates the terms of the treaty.