Key dates in the history of nuclear weapons development in North Korea:
1986: North Korea begins operations of a 5-megawatt reactor at Yongbyon built with Soviet help.
1993: North Korea announces it will quit the Nuclear Nonproliferation Treaty, later suspends its withdrawal.
1994: North Korea and the United States sign an agreement in Geneva. The North pledges to freeze - and eventually dismantle - its plutonium-based nuclear weapons programme in exchange for help building two power-producing nuclear reactors.
September 17, 1999: Bill Clinton, the US president, agrees to first major easing of economic sanctions against North Korea since the Korean War's end in 1953.
October 23-24, 2000: Madeleine Albright, the US secretary of state, visits Pyongyang, the highest-ranking US official ever to visit North Korea.
January 29, 2002: George Bush, the US president, labels North Korea, Iran and Iraq an "axis of evil."
October 4, 2002: North Korea tells visiting US delegation it has a uranium enrichment programme, Washington says.
November 11, 2002: US and Asian allies - Japan, South Korea - halt oil supplies to the North promised in the 1994 deal and suspend construction of two new reactors.
January 10, 2003: North Korea says it will withdraw from the Nuclear Nonproliferation Treaty.
August 27-29, 2003: North Korea joins first round of six-nation talks, involving envoys from China, Japan, Russia, the US and South Korea.
February 25-28, 2004: Second round of six-nation talks.
June 23-26, 2004: Third round of six-nation talks.
February 10, 2005: North Korea announces it has nuclear weapons.
July 26, 2005: Fourth round of six-nation talks is held, ending in recess after 13 days with no agreement.
September 13, 2005: Six-nation talks resume.
September 15, 2005: US blacklists Macau-based bank for alleged counterfeiting and money-laundering by North Korea, leading the bank to freeze North Korean assets.
September 19, 2005: North Korea promises to dismantle nuclear programmes in exchange for pledges of energy assistance; US says it has no plans to invade, and will respect North's sovereignty in an agreement ending talks.
November 9-11, 2005: Fifth round of six-nation talks.
January 3, 2006: North Korea says it will not return to talks unless the US lifts financial restrictions imposed in 2005.
July 5, 2006: North Korea launches seven missiles - including a long-range model - into the Sea of Japan, drawing international condemnation and a UN Security Council resolution condemning the act.
October 9, 2006: North Korea says it has conducted its first-ever nuclear test.
October 14, 2006: UN Security Council unanimously adopts a resolution imposing wide-ranging economic and diplomatic sanctions on North Korea for its nuclear test.
December 18-22, 2006: Six nations envoys meet in wake of nuclear test, no breakthrough made.
January 16-18, 2007: US and North Korean envoys meet in Berlin.
February 8-13, 2007: Six-nation talks resume in Beijing, a tentative agreement on disarming Pyongyang is reached. The draft plan contains commitments on disarmament and energy aid along with "initial actions" to be taken by certain deadlines.
July 14, 2007: North Korea says it has shut down the Yongbyon reactor.
September 6, 2007: Israeli plans attack and destroy a site in Syria. After months of speculation the US later says the site was a nuclear reactor under construction with North Korean help, following a design similar to the Yongbyon plant.
November 2007: North Korea begins disabling Yongbyon reactor under surpervision of international - including US - experts.
December 31, 2007: North Korea misses agreed deadline for it to submit a full declaration of all its nuclear activities.
May 2008: North Korea hands US officials more than 18,000 pages of records on the Yongbyon plant. The US later says it will provide 50,000 tons of much-needed food aid to North Korea as a humanitarian gesture.
June 26, 2008: North Korea hands over much-delayed declaration of nuclear activities. US announces it will remove North Korea from list of state sponsors of terrorism.
June 27, 2008: In a symbolic gesture of its commitment to ending its nuclear programme, North Korea destroys the cooling tower at its Yongbyon nuclear plant. The reactor itself had already been disabled.
July 12, 2008: Negotiators from six nations agree on steps to verify nuclear disarmament. North Korea is to finish disabling Yongbyon by the end of October while the US, China, Russia, Japan and South Korea would complete deliveries of fuel oil and other economic aid.
July 24, 2008: Condoleezza Rice, the US secretary of state, and Pak Ui-chun, North Korea's foreign minister, meet during the highest level of diplomatic contact between the two countries in four years, to reaffirm commitments to nuclear disablement.
August 26, 2008: North Korea announces reversal of disablement work at Yongbyon facilities in response to the US' refusal to remove Pyongyang from its list of state sponsors of terrorism.
October 11, 2008: The US says it will take the North off the list following a verbal agreement it will continue dismantling the nuclear plant.
February 23, 2009: Sorth Korea says North Korea has a new type of ballistic missile capable of reaching northern Australia and the Pacific island of Guam.
April 5, 2009: North Korea launches a rocket carrying what it insists is a communications satellite, but the move draws accusations it was testing a long-range missile. The UN Security Council responds by imposing further sanctions.
April 14-25, 2009: North Korea announces move to quit six-party nuclear talks and re-start operations at partly-disabled Yongbyon. It also expelled UN inspectors, and later announced that the reprocessing of spent fuel rods has begun.
April 29, 2009: Angered by criticisms over its rocket launch, the North threatens to conduct nuclear test and test long-range ballistic missile unless the UN Security Council apologises for imposing sanctions.
May 7-12, 2009: Special US envoy on North Korea visits Asia, saying Washington is ready for direct talks with Pyongyang. But the North dismisses the offer as useless, citing the US' "hostile policy".
May 25, 2009: North Korea confirms successful underground nuclear test, raising the explosive power and level of control of its nuclear device. The test raises regional tensions and draws international condemnation.
Source: Al Jazeera