North Korea on Friday announced a "successful" nuclear test, its fifth and the second this year. Following is a chronology of the country's nuclear development:
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December 12, 1985 -- North Korea joins the Nuclear Non-Proliferation Treaty (NPT).
March 12, 1993 -- Pyongyang declares its withdrawal from the NPT, but later allows inspectors of the International Atomic Energy Agency to inspect nuclear-suspected sites.
October 21, 1994 -- Pyongyang and Washington sign the Geneva agreement in which North Korea pledges to freeze its nuclear programme in return for US aid to build two light-water reactors.
December 2002 -- Washington declares to stop providing heavy oil to Pyongyang, which expels IAEA inspectors and removes monitoring equipment in retaliation.
January 10, 2003 -- Pyongyang officially withdraws from the NPT.
September 19, 2005 -- A joint statement was announced after a marathon dialogue between the six parties: North, South Korea, China, the US, Russia and Japan. Pyongyang pledges to abandon all nuclear weapons and relevant nuclear programme, while Washington promises the normalization of relations with Pyongyang, non-aggression against the country as well as economic assistance.
July 5, 2006 -- The country test-fires a Taepodong-2 missile on US Independence Day, but it appears to have failed.
October 9, 2006 -- Pyongyang conducts its first atomic bomb test in an underground facility.
February 13, 2007 -- North Korea returns to the six-party talks, agreeing to close its nuclear facility in exchange for normalized ties with the United States and economic assistance.
June 27, 2008 -- Pyongyang destroys a water cooling tower at its main Yongbyon nuclear facility in a symbolic gesture.
December 8-11, 2008 -- Pyongyang walks out from the six-party talks due to disputes over how to verify its nuclear abandonment.
April 5, 2009 -- Pyongyang launches an Unha-2 rocket, which Seoul and the international community denounces as a test of ballistic missile technology.
May 25, 2009 -- North Korea conducts its second nuclear test. Its explosive yield is estimated at 3-4 kilotons.
April 13, 2012 -- Another launch of an Unha-3 rocket is conducted but it fails. Seoul and Washington blast it as a cover-up for long-range missile test.
December 12, 2012 -- Pyongyang successfully launches a long-range Unha-3 three-stage rocket from the Sohae Space Centre.
February 12, 2013 -- A third nuclear detonation is carried out in its main Punggye-ri underground test site. It is the first atomic device test under top leader Kim Jong Un. Its explosive yield is estimated at 6-7 kilotons, with highly-enriched uranium believed to be used as nuclear material.
January 6, 2016 -- Pyongyang tests what it claims the first hydrogen bomb, the fourth of its nuclear detonations. The purported thermonuclear test triggers toughest-ever UN Security Council sanctions.
February 7, 2016 -- Pyongyang launches a Kwangmyongsong long-range rocket.