The Democratic People's Republic of Korea (DPRK) announced on Monday it has successfully conducted "one more" underground nuclear test earlier in the day.

Here is a brief introduction of the nuclear issue on the Korean Peninsula.

The nuclear issue on the Korean Peninsula surfaced in the early 1990s, when the United States, based on its satellite information, suspected that the DPRK had facilities for the development of nuclear weapons.

Pyongyang denied the allegation, saying it had neither the intention nor the capability to develop nuclear weapons. It also criticized the U.S. for deploying nuclear weapons in South Korea, which served as a threat to DPRK's security.

From May 1992 to Feb. 1993, the DPRK accepted six irregular inspections by the International Atomic Energy Agency.

The DPRK and the U.S. signed the Framework Agreement in Geneva in October 1994. Under the accord, Pyongyang agreed to freeze its nuclear program in exchange for the construction of light-water reactors and fuel oil provided by a U.S.-led Korean Peninsula Energy Development Organization to make up for the loss of electric power in the DPRK due to the suspension of its nuclear plan.

In October 2002, the U.S. said the DPRK had admitted that it had a program to enrich uranium after U.S. special envoy James Kelly visited the country. The DPRK responded by claiming that it had the right to develop nuclear weapons and weapons even more powerful.

In December 2002, the U.S. stopped shipping fuel oil deliveries to the DPRK, charging that the DPRK had violated the Geneva accord. In response, the DPRK announced an end to its nuclear freeze, removed the seals and monitoring cameras from the frozen nuclear facilities installed by the IAEA and restarted the nuclear facilities used for producing electricity.

Moreover, the DPRK released a statement in January 2003, announcing its withdrawal from the nuclear Non-Proliferation Treaty while claiming it had no intention to develop nuclear weapons.

The Chinese government has made positive efforts for a peaceful solution for the nuclear issue on the Korean Peninsula and finally brokered the six-party talks involving China, the DPRK, the United States, South Korea, Russia and Japan.

The first round of the six-party talks on the Korean Peninsula nuclear issue was held in Beijing in August 2003, in which the principle of peacefully resolving the nuclear issue through negotiations had been established.

On Feb. 13, 2007, the third phase of the fifth round of the six-party talks ended in Beijing with a joint statement on the first step toward the denuclearization of the Korean Peninsula. In July the same year, the DPRK closed and sealed its nuclear facilities in Yongbyon.

On October 3, the second phase of the sixth round of six-party talks released a joint document, named the Second-Phase Actions for the Implementation of the Joint Statement, under which the DPRK and the United States remain committed to improving their bilateral relations and moving toward a full diplomatic relationship.

In November, the DPRK began to disable three nuclear facilities in Yongbyon. However, the agreement reached on Oct. 3 had not been effectively implemented due to a divergence on the nuclear declaration between the DPRK and the U.S.

In June 2008, the DPRK destroyed the cooling tower at its Yongbyon nuclear complex, marking a symbolic step forward towards the denuclearization on the Peninsula.

On April 5, 2009, the DPRK carried out a rocket launch, arousing serious concern of various sides.

The UN Security Council on April 13 adopted a presidential statement on the April 5 launch by the DPRK, saying it is "in contravention of Security Council resolution 1718" and urging the early resumption of the six-party talks.

Pyongyang subsequently announced it was quitting the six-party talks on nuclear disarmament and would restart nuclear facilities in protest of the UN statement.

On May 25, the DPRK announced it has successfully conducted the second underground nuclear test, following with a short-range missile launch in the same day.

Source: Xinhua