N Korea pressed on nuclear programme

North Korea already has long-range missiles

The United States is mobilising international pressure on North Korea to drop its alleged nuclear weapons programme.

Speaking on a visit to South Korea on Saturday, American envoy James Kelly said the US would work with South Korea, Japan and other countries for the "immediate and visible dismantling" of North Korea's reported project to build nuclear bombs.

This is a difficult and complex problem

James Kelly, US Assistant Secretary of State

The assistant secretary of state held talks with South Korean officials about co-ordinating a response to what America sees as the nuclear threat posed by North Korea.

It comes days after America said North Korea admitted to pursuing a nuclear weapons programme.

His visit to Seoul coincides with a previously arranged visit to North Korea by a South Korean delegation, led by South Korean Unification Minister Jeong Se-Hyun.

Mr Se-Hyun said he would "have straight talk" about the nuclear issue with North Korean officials.

No deadline

Mr Kelly said the United States was now consulting its allies on the next step, but said there was no deadline for the issue.

Kelly wants to build up a united front

"This is a difficult and complex problem... we'll just have to see how it unfolds, " he told reporters at a news conference.

The assistant secretary of state arrived from Beijing, where he consulted Chinese leaders.

He is due to go to Japan on Sunday.

Mr Kelly said the United States was committed to a "peaceful Korea free of nuclear weapons", adding that the US had not warned South Korea of any repercussions if it refused to abandon its nuclear ambitions.

He said the United States would keep diplomatic channels open but would not repeat the negotiating process that followed the last confrontation with North korea in 1994.

A South Korean Government official said concrete steps to tackle the issue will be determined between the US, South Korea and Japan at the Asia Pacific Economic Co-operation (Apec) forum in Mexico later this month.

'Not so favourable'

The BBC's Charles Scanlon, in Seoul, says the South Korean Government has stressed the need to continue dialogue but the United States is taking a tougher line.

A 48-strong South Korean delegation arrived in Pyongyang on Saturday for four days of talks with a North Korean delegation led by Chief Cabinet Minister Kim Ryong-song.

South Korea: We will tell the North clearly what we think

The meeting had originally been intended to cover co-operation between the peninsula's two states but the nuclear issue is expected to dominate the agenda.

Mr Jeong remarked before leaving that the circumstances for the talks were "in many ways not so favourable".

After a dinner on Saturday, the two delegations are expected to begin full talks on Sunday.