Mohamed ElBaradei, director general of the International Atomic Energy Agency (IAEA), also said the agency would dispatch one or two more teams this month to look into South Korea's past record of clandestine nuclear tests.

"We have not seen any cover-up," ElBaradei told a news conference.

"We are getting good cooperation from the South Korean government."

North Korea, citing concern about Seoul's nuclear experiments among other issues, has put on hold multilateral talks aimed at defusing tensions over its own atomic weapons drive.

North Korea has accused the United States of applying double standards concerning the nuclear issues of the two Koreas but ElBaradei said there were no parallels between the two cases.

"North Korea has a full-fledged reprocessing plant operating while South Korea has been continuously under safeguard and under verification," he said, noting that North Korea had reneged on its commitments to comply with non-proliferation safeguards.

"We wish to resolve both issues as quickly as possible. We expect the South Korean issue to be resolved much quicker ... Since (it is) complicated, the North Korean issue will take much longer time," said the IAEA chief, who is here for an anti-nuclear weapons proliferation conference.

The IAEA sent inspectors here twice last month after Seoul revealed that its scientists secretly enriched a tiny amount of plutonium in 1982 and uranium in 2000.

South Korea says the laboratory experiments with potential ingredients for bombs were not linked to nuclear weapons programs. ElBaradei had expressed "serious concern" about the activities.

He said the IAEA would send more teams this month to South Korea.

"We are going to have one mission or two this month," ElBaradei said, adding that he expected to report to IAEA members about the outcome of the inspections in November.

He warned against any hasty conclusion on South Korea. "It is pretty dangerous to jump to a conclusion. You'll be in a better position to judge when we are through with our investigation," he said.

The IAEA chief repeated his call for North Korea to return to the Non-Proliferation Treaty (NPT), an international convention aimed at preventing the spread of nuclear weapons, and said he wished to see progress in the six-way talks on Pyongyang's nuclear ambitions.

"People in the international community are getting impatient to see ... North Korea turn back to the nonproliferation regime," he said.

Little progress has been made during the past three rounds of six-nation talks aimed at frustrating North Korea's nuclear ambitions. A fourth round was scheduled for September, but was boycotted by North Korea.