South Korea is calling North Korea's uranium enrichment program "worrisome."
Foreign Minister Yu Myung-hwan said in Seoul Monday the United Nations might discuss how to handle the uranium issue. He did not elaborate.
North Korea announced last month it has entered the final stage of enriching uranium. That would give Pyongyang a second way to make nuclear bombs, in addition to its plutonium-based program.
North Korea has signaled it is ready to return to international talks on its nuclear weapons program, if it gets to talk one-on-one with the United States.
South Korea's foreign minister expressed skepticism about North Korea's motives. He said there are no real grounds to believe the softening stance indicates a fundamental change in Pyongyang's position.
The U.S. and South Korean defense chiefs will discuss Pyongyang's nuclear threat in Seoul Thursday.
The United States has suggested it would be open to talks with North Korea, as long as the talks are in the context of the multilateral negotiations that also involve South Korea, China, Russia and Japan.
On Friday, the U.S. State Department said it approved a rare visa for senior North Korean diplomat Ri Gun. The envoy plans to attend a conference in the United States. Analysts see the visit as a potential opportunity to set up talks.
On Monday, North Korea's Rodong Sinmun newspaper urged South Korea to end its "confrontation" with the North.