The pro-Russian prime minister of Ukraine's semi-autonomous Crimea region has claimed control of all military, police and other security services in the region and appealed to Russia's president for help in keeping peace there.
Sergei Aksenov said on Saturday that servicemen from Russia's Black Sea fleet were guarding important buildings in the Black Sea peninsula, Russia's Interfax news agency reported.
In a statement Aksenov declared that Crimea's armed forces, the police, the national security service and border guards will answer only to his orders.
He said any commanders who do not agree should leave their posts.
Meanwhile, the International airport at Simferopol, the main city in Crimea, said its airspace was closed and there were no flights to or from the airport.
"Due to limitations in the use of the airspace, the airport has temporarily suspended receiving flights," the airport said in a written statement, Reuters news agency reported. Armed men took control on the airport on Friday.
In Moscow, Russia's Lower House of Parliament, the Duma, asked Russian President Vladimir Putin to take measures to stabilise the situation in Crimea, Interfax cited the speaker of the Duma as saying.
"The Duma Council adopted an appeal to the president of Russia, in which parliamentarians are calling on the president to take measures to stabilise the situation in Crimea and use all available means to protect the people of Crimea from tyranny and violence," Interfax cited Sergei Naryshkin as saying.
Ukraine on Friday accused Russia of a “military invasion and occupation'' - a claim that brought an alarming new dimension to the crisis, and raised fears that Moscow is moving to annex a strategic peninsula where Russia's Black Sea fleet is based.
In response to that, Ukraine's new prime minister on Saturday said his country would not be drawn into a military conflict by Russian "provocations" in the Crimea region and renewed his appeal to Moscow to halt military movements there.
"It is unacceptable when armoured Russian military vehicles are out in the centre of Ukrainian towns," Prime Minister Arseny Yatseniuk said before a government meeting in the Ukrainian capital, Kiev.
The newly formed government in Kiev accuses Russia of deploying 2,000 troops to the Crimean region, which has a majority of ethnic Russians and is defying the oust of Moscow-backed Ukrainian leader Viktor Yanukovich.
Ukraine's defence minister said Russia had "recently" brought 6,000 additional personnel into Ukraine and that the Ukrainian military were on high alert in the Crimea region.
Moscow, denying accusations of staging an aggression against its neighbour country and former member the Soviet union, said any military movement in Crimea is part of an agreement that was previously made.
This comes after US President Barack Obama warned arch foe Putin his country would pay "costs" if it is to stage a military intervention.
Obama said Friday he is "deeply concerned by reports of military movements taken by the Russian Federation inside of Ukraine".
Government buildings, including two airports, in the semi-autonomous Crimea region, have had the Russian navy flag marking their roofs after pro-Kremlin armed men took control late Thursday.
Obama and other world leaders are looking into "possible repercussions" if Russia were to militarily intervene in Ukraine, a former member of the dissolved Soviet union, Al Jazeera's Rosiland Jordan reported from Washington DC, quoting a White House official.
Options include skipping a G8 summit planned for this summer in Sochi, Russia, as well as trade limitations "and putting some commerce deals on hold," Al Jazeera's Jordan reports.
"There are no discussions, so far, of a military response, as it is hoped that the crisis would be solved through words and no weapons," she added.
But as Russia denies any wrongdoing, the crisis is unlikely to ease.
"You all know we have an agreement with Ukraine on the presence of the Russian Black Sea fleet with a base in Sevastopol, and we are acting within the framework of that agreement," Russia's UN Ambassador Vitaly Churkin said on Friday.
He made the statement after a closed-door UN Security Council emergency session which was called for by Kiev's new government to discuss developments in Crimea.
"The best way to resolve the crisis is to look hard again at the February 21 agreement," Churkin said. "They need to have a constitutional dialogue and process of forming a new constitution. They need to refrain from conducting a hasty presidential election which most likely will create more friction within the country. They need to stop trying to intimidate other regions and other political forces."
Ukraine's new government, which came to power after the ousting of Russia-backed President Viktor Yanukovich, has called for fresh presidential elections on May 25.