Nuclear researchers affiliated with the Korean Atomic Energy Research Institute were "eager to reprocess plutonium from spent fuel ... to reduce S. Korea's high dependence on imported fossil fuels, and, increasingly, on uranium fuel," reported the Nonproliferation Review in 2001.

Seeking to stabilize the always tense Korean peninsula, the United States put pressure on the Koreans to end their nuclear work. In 1975, the Seoul government agreed to American demands and ended its program and signed the nuclear Non-Proliferation Treaty in April. That deal was quickly followed by a pact that established a full set of International Atomic Energy Agency safeguards in November of that same year.

After more than 20 years of relative quiet, in 1997 IAEA inspectors found two particles of slightly depleted uranium in plutonium samples taken from a research reactor in Seoul, which indicated that plutonium separation tests had been conducted. When confronted by the IAEA in 1999, South Korea denied that experiments had taken place.

Concerns continued to grow after South Korea barred IAEA inspectors' access to its nuclear sites in 2001. Finally the IAEA confronted the government in 2003.

In 2004, South Korea disclosed to the IAEA that it had conducted a plutonium experiment in 1982 and a uranium enrichment experiment in 2000 without informing the IAEA. In a statement to the IAEA, South Korean officials said that the 2000 experiments "were carried out without the government's knowledge." The country then allowed IAEA weapons inspectors to visit its nuclear research facilities and to conduct interviews with relevant scientists.

The IAEA reported South Korea's disclosure to the world in September 2004 and IAEA chief Mohamed ElBaradei said in November, "with regard to the Republic of Korea (South Korea), we are saying that although the materials have not been significant, the nature of the activities, enrichment and reprocessing are a matter of serious concern. However, we are also saying that we have not seen any continuation of these experiments, which is the good news."

South Korea's NPT violations were reported in The Washington Post as having "thrown the Bush administration's efforts on Iran and North Korea into turmoil." The United States, which has strongly opposed North Korea's nuclear program and called for sanctions against Iran's uranium enrichment activities, was accused of being soft on its ally South Korea.

U.S. Secretary of State Colin Powell said in October that there was no comparison with secret nuclear experiments carried out by South Korea in the past and ongoing atomic programs in North Korea and Iran.

"South Korea's experiments to extract plutonium in 1982 and to enrich uranium in 2000 do not indicate a present and dedicated effort to develop nuclear weapons. However, the experiments could have broad implications given South Korea's past nuclear weapons development program and the ongoing efforts to thwart North Korea's nuclear ambitions," wrote Daniel Pinkston, a senior research associate and Korea specialist at the Center for Nonproliferation Studies, in 2004.

North Korea boycotted a new round of six-nation talks and said that "talks with Washington and others aimed at ending [North Korea's] nuclear ambitions must be tied to a full investigation of South Korea's work," reported The Washington Post.

The United States government has said it will treat any South Korean violations in the same manner as North Korean violations.

"One thing I can assure is that we will not allow a double standard," then-Undersecretary of State for Arms Control and International Security John Bolton said in 2004.

-- Compiled by Wendy Mbekelu for the Online NewsHour