ElBaradei's trip to South Korea, where he is due to address a conference in Seoul, was scheduled before news broke of South Korea's activities, according to International Atomic Energy Agency (IAEA) spokeswoman Melissa Fleming.

"He's also using the opportunity to take up a longstanding invitation by South Korea to make a bilateral state visit. There are a number of topics he wishes to discuss and of course he understands that the recent revelation about nuclear experiments will come up in the discussions," Fleming said.

IAEA inspectors were last week in South Korea to investigate Seoul's past secret experiments involving potential ingredients for nuclear bombs.

Yonhap news agency said inspectors had taken about 20 samples of nuclear material and waste back to the IAEA's headquarters in Vienna.

Seoul revealed in September that its scientists secretly enriched a tiny amount of plutonium in 1982 and uranium in 2000.

South Korea says the laboratory experiments were not linked to nuclear weapons programs. ElBaradei, however, has expressed "serious concern" about the activities.

ElBaradei travels Wednesday to Japan, where he will be on Friday when the Nobel Peace Prize is to be announced in Oslo.

Observers have said they expect the Nobel committee this year to hail efforts to halt nuclear arms proliferation, tapping as likely winners the IAEA and its chief ElBaradei.

After playing a vital role in the inspections of former Iraqi leader Saddam Hussein's weapons arsenal and the search for his suspected nuclear program, the IAEA is currently struggling to get Iran to halt controversial uranium enrichment-related activities and to get to the bottom of North Korea's secretive nuclear program.