Assistant Secretary of State Christopher Hill left for Vietnam, a US embassy spokesman said.

Mr Hill had arrived in the Chinese capital from Thailand, where he had said there was a possibility he could meet North Korea's Kim Kye Gwan in Beijing amid diplomatic efforts to keep a 2007 disarmament agreement on track.

'The meeting with Kim Kye Gwan did not take place,' said the embassy spokesman.

'He said he would not meet with Kim before he returns to Washington.' The spokesman said she did not know when Mr Hill would return to Washington.

Under a six-nation deal reached last year by the two Koreas, China, the United States, Russia and Japan, the North was supposed to disable its main atomic plants and declare all of its nuclear programmes by December 31.

Pyongyang has said it submitted a full list in November, but the United States insists it is still waiting for the complete declaration, including a full account of a suspected covert uranium enrichment programme.

Mr Hill was in Beijing in mid-February for talks with Kim but emerged from the meeting with no report of progress.

In the Chinese capital last week, visiting US Secretary of State Condoleezza Rice urged Beijing - North Korea's closest friend in the world - to use 'all influence possible with the North Koreans' to see that the agreement is met. -- AFP