South Korea says it is looking into reports there may be additional uranium enrichment facilities in North Korea, in addition to its main nuclear complex at Yongbyon.
South Korea's foreign minister says the government is well aware of the possibility that North Korea has additional uranium reprocessing facilities.
Kim Sung-hwan on Tuesday said there are intelligence reports about this but he would not go into specifics.
The foreign minister says he suspects that what experts have said about North Korea having other enrichment sites is correct.
A U.S. scientist was shown one complex at Yongbyon last month. Stanford University professor Siegfried Hecker proclaimed the operation surprisingly sophisticated, apparently with hundreds of working centrifuges to enrich uranium.
Hecker, in an article published in Foreign Affairs magazine last week, said the centrifuge facility he visited was probably designed to build a reactor, not a bomb. But Hecker said it is highly likely a covert facility exists elsewhere in North Korea capable of producing highly enriched uranium.
That would give North Korea an additional method of making nuclear bombs in addition to a plutonium operation.
A South Korean newspaper on Tuesday quoted an unidentified intelligence official here as saying it is likely there are other undisclosed locations where Pyongyang secretly enriches uranium.
Suspected facilities include a research institute in downtown Pyongyang, a missile base in Yanggang province and a cave at Kumchangri, 160 kilometers north of the capital.
Analysts say the communist state has repeatedly provided glimpses of its efforts to make nuclear weapons, partly to prod other countries into negotiations to extract badly needed aid for its impoverished economy.
But talks that began in 2003 to persuade Pyongyang to give up its nuclear programs in return for aid and greater diplomatic recognition have stalled for two years. The Koreas, China, Japan, Russia and the United States are involved in the talks.
Tensions have soared on the Korean peninsula this year. North Korea is blamed for the sinking in March of a South Korean warship, killing 46 sailors. Pyongyang denies involvement.
Last month, North Korea shelled an inhabited South Korean island, killing four people.
Diplomats from various countries, including the U.S. and China, are shuttling among capitals to discuss North Korea. U.S. diplomats are visiting Beijing, Seoul and Tokyo this week. And delegations from both Koreas are in Moscow this week.
Despite the diplomacy, the U.S., South Korea and Japan have been cool to China's suggestion of emergency talks with North Korea.