Senior United States and South Korean officials on Tuesday began debating a strategy for progress in upcoming talks on North Korea's nuclear programme, as well as ways to keep up the pressure on the communist regime.
Undersecretaries of State Nicholas Burns and Robert Joseph arrived from Japan and will go on to China to stress the importance of a united front when six-nation talks resume after a year-long break.
Joseph was also discussing ways to enforce UN sanctions imposed on the North after its October 9 nuclear test.
South Korea, like other UN member states, must submit a list of its own measures against Pyongyang by early next week.
But it has stopped short of supporting tough action proposed by Japan and the United States.
Just three weeks after the test, North Korea announced it would end a year-long boycott and return to the nuclear disarmament talks.
But both Japan and the United States have called for "concrete" action by North Korea to end its nuclear programme when talks resume, possibly this month or next.
The forum, which began meeting in 2003, groups the two Koreas, Japan, China, the United States and Russia.
"It's clear that the United States and Japan see eye to eye on the question of North Korea," Burns said in Tokyo on Monday after meeting Foreign Minister Taro Aso.
Joseph added: "We are in agreement that the (sanctions) resolution must be fully and effectively implemented until North Korea meets all of the demands of the Security Council.