U.S. envoy James Kelly has wrapped up a trip to Asia where he discussed the North Korea nuclear crisis and tried to line up another round of six nation talks.

The Assistant U.S. Secretary of State for East Asian and Pacific Affairs has concluded a three-nation tour to Japan, China and South Korea. His goal was bringing those nations and others together for a second round of talks to get North Korea to freeze its nuclear programs.

James Kelly gave no details Friday about his meetings with South Korean officials, the last of his trip.

Mr. Kelly left Seoul for Washington, where his diplomatic push for the six-nation talks will continue. Analysts and diplomats are speculating that the talks could happen as early as December, but Mr. Kelly warned Wednesday that prospects for new talks before year-end remain uncertain.

South Korean Assistant Foreign Minister Lee Soo-hyuck said Friday that he and the U.S. envoy had discussed the wording of a written security assurance for North Korea. Mr. Lee said they had progressed to "working out details, rather than outlines" of a blueprint to end the nuclear crisis.

Pyongyang has said it would consider a security guarantee, a proposal first offered by President Bush, as a basis for continuing talks. Earlier, the North had demanded a bilateral non-aggression treaty with Washington, but U.S. officials rejected the demand.

A first meeting, which included the United States, China, South Korea, North Korea, Russia and Japan, took place in Beijing in August but ended inconclusively.

After that meeting, North Korea indicated it did not want to participate in further multinational talks, but has since told its ally China that it might come to the negotiating table.

The dispute over North Korea's nuclear activities has gone on for more than a year. In October last year, U.S. officials said Pyongyang admitted it was trying to enrich uranium for nuclear bombs and it has since kicked out United Nations nuclear inspectors and withdrawn from the nuclear Non-Proliferation Treaty.

It also says it has reprocessed 8,000 spent nuclear fuel rods to make more weapons. Western intelligence experts have been unable to verify the claim.