North Korea's state news agency announced on Monday that the country had conducted its first nuclear test, less than a week after Pyongyang threatened to do so.

Following is a chronology of major milestones in the North Korean nuclear crisis:

October 2002: Top State Department envoy James Kelly confronts Pyongyang with evidence Washington says points to a covert uranium-enrichment programme. North Korea says "it is entitled to possess not only nuclear weapons but other types of weapons more powerful than them in defence of its sovereignty in face of the U.S. threat".

December 2002: North Korea says it plans to restart Yongbyon reactor, disables International Atomic Enegy Agency (IAEA) surveillance devices at Yongbyon and expels IAEA inspectors.

January 2003: North Korea says it is quitting the nuclear Non-Proliferation Treaty with immediate effect.

At talks between U.S. team led by Kelly and North Koreans and China in Beijing, American officials say North Korea told the United States that it has nuclear weapons and might test them or transfer them to other countries.

August 2003: First round of six-way talks between North and South Korea, China, Japan, Russia and the U.S. on the nuclear issue takes place in Beijing. North Korea threatens to test nuclear bomb and test-fire new missile. 

October 2003: North Korea says it has enhanced its "nuclear deterrent" with plutonium reprocessed from thousands of nuclear fuel rods. Pyongyang says it is willing to display the deterrent.

January 2004: Pyongyang permits unofficial U.S. delegation, including nuclear expert, to tour Yongbyon. U.S. nuclear expert Sigfried Hecker says he is not convinced North Korea could turn its nuclear technology into a weapon or mount it on a missile. 

February 2004: Father of Pakistani nuclear bomb, scientist Abdul Qadeer Khan, admits he passed on uranium-linked technology to Libya, Iran and North Korea. Pyongyang calls the confession a lie.

Second round of six-party talks held in Beijing.

June 2004: Third round of talks take place in Chinese capital. U.S. proposes fuel aid and security guarantees to North Korea if it scraps nuclear programmes.

February 10, 2005: North Korea's Foreign Ministry issues statement saying country has manufactured nuclear weapons for self-defence and is quitting six-way talks indefinitely.

June 17: North Korean leader Kim Jong-il tells senior South Korean envoy in Pyongyang that North Korea can return to talks as early as July, if United States meets certain conditions, such as treating North Korea with "respect".

July 9: North Korea announces it has agreed to return to stalled talks in last week of July.

July 22: North Korea calls for peace treaty to replace armistice that ended hostilities in 1950-53 Korean War, saying it would resolve nuclear crisis. 

July 26: Six-party envoys begin fourth round of talks.

Parties all push to issue joint statement, but talks deadlock as North Korea insists on having civilian nuclear energy.

August 7: Marathon fourth round goes into recess after running 13 days, longer than all previous sessions.

August 23: Top U.S. negotiator Christopher Hill says issue of North having civilian nuclear plan would not break deal.

September 13: Fourth-round talks resume in Beijing.

September 19: Six parties issue long-awaited joint statement.

North Korea promises to give up its nuclear weapons and programmes. In exchange, other parties express willingness to provide oil, energy aid and security guarantees. Agreement says North Korea could have nuclear energy programme in future if it meets strict safeguards.

November 9: Fifth round of talks in Beijing break off without progress. North Korea later protests the U.S.'s freezing of its funds in a Macau.

July 5, 2006: North Korea launches seven missiles from its east coast, including the long-range Taepodong-2.

October 3: North Korea's Foreign Ministry says the country will conduct its first nuclear test but gives no date.

October 9: State Korean Central News Agency (KCNA) reports North Korea has conducted a successful underground test.