The following is a chronology of major events leading to North Korea's third underground nuclear test on Tuesday.

▲2006

July 4: North Korea test-fires at least six missiles, including a long-range Taepodong-2, despite a chorus of international warnings.

July 5: North Korea test-fires a seventh missile, despite international condemnation of its earlier launches.

July 17: The U.N. Security Council unanimously votes to impose sanctions on North Korea over the missile tests. The resolution bans U.N. members from trading missile-related materials to the communist state.

Oct. 9: North Korea says it successfully carried out its first-ever test of a nuclear device.

Oct. 15: The U.N. Security Council votes unanimously to impose weapons and financial sanctions on North Korea over its nuclear test. Resolution 1718 demands Pyongyang to eliminate all its nuclear weapons, weapons of mass destruction and ballistic missiles.

Dec. 18: Six-party denuclearization talks resume in Beijing, attended by the two Koreas, U.S., China, Japan and Russia. Talks end with no sign of progress.

▲2007

Feb. 8: Six-party denuclearization talks resume in Beijing.

Feb. 13: Pyongyang agrees to shut down its nuclear reactor and invite international inspectors within 60 days in return for massive energy assistance.

March 13: Mohamed ElBaradei, secretary general of the International Atomic Energy Agency (IAEA), visits Pyongyang for talks.

March 14: The U.S. Treasury Department bans American financial institutions from dealing with the Macau-based Banco Delta Asia (BDA), suspected of handling illicit North Korean assets.

March 22: Six-party talks open, picking up where the Feb. 13th agreement left off after Pyongyang walked out over talks of frozen funds in BDA.

April 14: North Korea misses the deadline to shut down the Yongbyon nuclear reactor in exchange for energy aid, citing about

US$25 million in frozen North Korean funds in BDA.

June 12: Russia offers to facilitate the fund transfer, paving the way for North Korea to fulfill a denuclearization deal that was overdue.

June 25: North Korea says it received its funds held in BDA.

June 26-30: IAEA inspectors arrive in North Korea to discuss freezing its nuclear reactor, the first time they have been allowed into the country since 2002.

July 15: North Korea says it has shut down its nuclear reactor after receiving the first shipment of 50,000 tons of heavy fuel oil. IAEA inspectors arrive for a monitoring visit to the Yongbyon nuclear reactor.

Sept. 2: Following bilateral talks in Geneva, the U.S. says North Korea has agreed to declare and dismantle all its nuclear facilities by the end of the year.

Sept. 3: North Korea says Washington has agreed to take it off from a list of countries that sponsor terrorism.

Sept. 11-15: A team of nuclear scientists from the U.S., China and Russia visit North Korea to inspect the dismantling of reactors and other facilities.

Nov. 1-5: American nuclear experts enter process to disable the reactor.

Nov. 27-27 Nuclear experts visit Yongbyon to inspect North Korea's denuclearization process.

▲2008

March 28: North Korea test-fires short-range missiles off its western coast.

June 26: After a delay of more than six months, the North hands over an account of its nuclear program.

June 27: North Korea explodes the cooling tower at its Yongbyon nuclear reactor, in a symbolic move to show its commitment to the talks on ending its nuclear program.

Aug. 26: Two months after submitting its nuclear declaration, Pyongyang says it has stopped disabling its nuclear facilities in protest of the delayed process to remove the country from the U.S. list of state sponsors of terrorism.

Sept. 24: The U.N.'s nuclear watchdog, the IAEA, says North Korea has removed seals preventing the use of its main plant at Yongbyon. North Korean officials say U.N. inspectors will have no further access to the plant.

Oct. 9: The U.N.'s nuclear watchdog says North Korea has banned its inspectors from entering the Yongbyon nuclear complex.

Oct. 11: The U.S. Department of State says it has taken North Korea off its list of state sponsors of terrorism, after the isolated country agreed to full verification of its nuclear sites.

Dec. 8-11: Latest round of six-party talks ends without agreement.

▲2009

April 5: North Korea launches a long-range rocket despite international condemnation, and was widely viewed as a covert test of its ballistic missile technology.

April 14: In response to U.N. Security Council condemnation of its rocket launch, North Korea announces that it will pull out of the six-party talks and orders IAEA inspectors to leave the country.

May 25: North Korea detonates an underground nuclear explosive device. This is North Korea's second nuclear test and is believed to be several times more powerful than the first one tested in 2006.

May 26: North Korea test-fires two short-range missiles hours after the U.N. Security Council condemned the nuclear test.

June 12: The U.N. Security Council votes unanimously to impose tougher sanctions on North Korea. The communist country strongly condemns the move.

Oct. 6: North Korea tells China it may be willing to return to the six-party talks, if it sees progress in bilateral talks with the U.S.

▲2010

March 26: North Korea torpedoes a South Korean warship near the tensely guarded western sea, killing 46 sailors. Pyongyang denies any involvement.

July 21: The U.S. announces new sanctions on North Korea, following the  sinking of a South Korean warship, targeting Pyongyang's sale and purchase of arms and import of luxury goods.

Aug. 30: U.S. President Barack Obama imposes new financial sanctions on North Korea, targeting its trade in arms, luxury goods and narcotics.

Nov. 12: Seigfried Hecker, a U.S. nuclear scientist, makes a visit to North Korea, where he is shown an advanced uranium enrichment plant in Yongbyon.

Nov. 23: North Korea shells South Korea's border island of Yeonpyeong, killing four people. The deadly provocation further raises tension on the peninsula.

▲2011

Aug. 1: Pyongyang says in a statement it is eager to resume the six-party talks without preconditions.

Oct. 25: The U.S. and North Korea fail to reach a deal on restarting negotiations on the North's nuclear program, after two days of talks in Geneva.

Nov. 30: North Korean state media says the construction of a light-water reactor and the production of low-enriched uranium are making progress.

Dec. 19: North Korea announces its long-time leader Kim Jong-il has died of a heart attack, aged 69.

Dec. 31: Kim Jong-il's youngest son, Jong-un, is formally named Supreme Commander of the Korean People's Army, state media says.

▲2012

Jan. 30: Seoul says it will allow a private group to deliver 180 tons of flour to North Korea.

Feb. 23: U.S. and North Korean officials meet in China for talks on Pyongyang's nuclear program, the first since the death of North Korean leader Kim Jong-il.

Feb. 29: North Korea agrees to suspend uranium enrichment as well as nuclear and long-range missile tests.

March 16: North Korea says it will launch a rocket to mark the 100th birthday of the country's late founder Kim Il-sung, the grandfather of Kim Jong-un.

April 13: North Korea launches a long-range rocket, but it flames out shortly after a lift-off.

April 16: The U.N. Security Council condemns North Korea's failed rocket launch in a statement.

Dec. 1: North Korea announces its plans to test another long-range rocket.

Dec. 12: North Korea successfully fires off a three-stage rocket and places the Kwangmyungsong-3 satellite into orbit. Seoul and Washington condemn the rocket launch as a covert test of its ballistic missile technology.

▲2013

Jan. 21: After examining debris from the first stage of the

Unha-3 rocket, South Korea's defense ministry says North Korea's December rocket launch was largely made using domestic technology.

Jan. 22: The U.N. Security Council passes a resolution condemning North Korea's rocket launch and tightens existing sanctions.

Jan. 24: North Korea's National Defense Commission says it will proceed with a "high-level nuclear test."

Feb. 4: North Korea's state media says its leader Kim Jong-un made an "important" decision regarding its security and sovereignty at a military meeting, amid mounting pressure on Pyongyang to scrap its plan for a nuclear test.

Feb. 12: North Korea conducts a third nuclear test in the Punggye-ri test site hours after the ruling Workers' Party Political Bureau vowed to continue to launch long-range rockets as part of an "all-out action of high intensity." (Yonhap News)