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North Korea apparently staged its third nuclear test on Tuesday, after the communist country vowed "high-intensity" action and further long-range rocket launches.
Here are key dates in its nuclear and missile programmes:
December 12: North Korea accedes to the nuclear Nonproliferation Treaty (NPT).
January 30: North Korea concludes a comprehensive safeguards agreement with the UN's International Atomic Energy Agency (IAEA).
February 9: The IAEA demands special inspections of two sites believed to store nuclear waste. North Korea refuses.
June 13: North Korea announces its withdrawal from the IAEA.
July 9: North Korean President Kim Il-Sung dies and is succeeded by his son, Kim Jong-Il.
October 21: The United States and North Korea adopt the "Agreed Framework". The North commits to freeze and eventually eliminate its nuclear facilities in exchange for two light water reactors (LWR) and heavy-fuel supplies.
August 31: North Korea launches a three-stage rocket called "Taepo Dong-1" with a range of 1,500-2,000 kilometres (930-1,240 miles) that flies over Japan.
September 7-12: North Korea agrees to a moratorium on testing long-range missiles.
December 15: Five years after the Agreed Framework, contract signed to begin construction of two LWRs in North Korea.
June 15: First-ever leaders' summit between North and South Korea. US relaxes sanctions on Pyongyang.
October 24: US Secretary of State Madeleine Albright meets Kim Jong-Il in Pyongyang.
January 29: US President George W. Bush characterises North Korea as part of an "axis of evil" along with Iraq and Iran.
October 16: The United States announces that North Korea admitted having a clandestine programme to enrich uranium for nuclear weapons.
November 14: Heavy-fuel oil deliveries to North Korea are suspended.
December 12: North Korea tells the IAEA it is restarting its one functional reactor and reopening other facilities frozen under the Agreed Framework.
December 22-24: North Korea cuts all seals and disrupts IAEA surveillance equipment on its nuclear facilities and materials.
December 27: North Korea orders IAEA inspectors out of the country.
January 10: North Korea announces its withdrawal from the NPT.
February 27: US officials confirm North Korea has restarted a five-megawatt nuclear reactor.
August 27-29: The first round of six-party talks is held in Beijing, grouping China, Japan, Russia, the United States and the two Koreas.
November 21: Suspension announced on construction of two LWRs.
February 10: North Korea's foreign ministry announces that Pyongyang has produced nuclear weapons.
September 19: Six-party talks deal commits North Korea to abandoning all nuclear weapons and programmes, and returning to the NPT.
July 4-5: North Korea test-fires seven ballistic missiles, including a failed test of its longest-range missile, the Taepo Dong-2.
July 15: UN Security Council resolution condemns the missile launches.
October 9: North Korea conducts first nuclear test underground.
October 14: UN Security Council imposes fresh sanctions on Pyongyang.
February 13: China announces deal under which North Korea will disable nuclear plants at Yongbyon and let IAEA inspectors return. It will get one million tonnes of fuel aid and be removed from a US list of terrorist states.
July 16: The IAEA confirms the shutdown of facilities at Yongbyon.
October 2-4: Second North-South Korea summit.
April 5: North Korea launches three-stage Unha-2 rocket.
April 13: UN Security Council presidential statement condemns rocket launch.
April 14: North Korea withdraws from six-party talks.
April 16: North Korea ejects IAEA and US monitors.
May 25: North Korea conducts its second underground nuclear test.
June 12: UN Security Council resolution expands sanctions on Pyongyang.
March 26: The South Korean patrol ship Cheonan is sunk near maritime border with North. Inter-Korean engagement frozen.
November 12: North Korea reveals uranium enrichment facility to visiting foreign experts.
December 17: North Korean leader Kim Jong-Il dies and is succeeded by his youngest son, Kim Jong-Un.
April 13: North Korea attempts to launch a satellite using the Unha-3, but the rocket falls apart after take-off.
December 12: North Korea successfully launches the Unha-3.
January 22: UN Security Council resolution expands existing sanctions.
January 24: The North announces its intention to conduct another nuclear test and continue rocket launches.
February 12: Pyongyang appears to detonate a nuclear device with regional monitors detecting an unusual seismic event, of a magnitude between 4.9 and 5.1, in the same location as the North's Punggye-ri nuclear test site. Seoul estimates the blast yield at six to seven kilotons.