Japan's top government spokesman on Friday voiced regret over South Korea's admission Thursday that its scientists enriched uranium four years ago.

"It is regrettable if it is true," Chief Cabinet Secretary Hiroyuki Hosoda told a news conference, a day after South Korea said it has disclosed that it conducted a secret uranium separation experiment in 2000 and it has no program for enrichment or reprocessing of nuclear materials.

Hosoda repeatedly stressed that since the circumstances and details of the program are "unclear", the Japanese government will take a wait-and-see attitude on how to address the issue.

"We will look at how discussions among the International Atomic Energy Agency (IAEA) and South Korea would go from the perspective of nuclear nonproliferation...before we pass judgment on the issue," he said.

Hosoda said the issue could "possibly be a subject for discussion in the "six-nation talks" -- which are scheduled for later this month -- but said he believes that it could be resolved to some extent by South Korea's explanations and IAEA discussions.

The Vienna-based IAEA has dispatched inspectors to investigate the matter, with a report due early next week.

South Korea said that the one-off experiment to separate a small amount of uranium -- 0.2 gram -- was isolated and part of laboratory-scale scientific research on production of nuclear fuel that was conducted in January and February 2000. The activities have since been halted.