BEIJING - US NUCLEAR envoy Christopher Hill arrived in Beijing on Friday for talks with his Asian counterparts, an official said, in an effort to determine whether North Korea had begun rebuilding its atomic plant.

North Korea last week announced that it had stopped disabling its Yongbyon nuclear complex, and would consider rebuilding it, because Washington had failed to drop it from a terrorism blacklist.

The news was a potential major setback for the six-nation talks - involving China, the United States, North and South Korea, Russia and Japan - that began in 2003 with the aim of ending the communist state's nuclear activities.

The Yongbyon reactor is at the heart of the North's decades-old nuclear weapons drive and produced the plutonium for its October 2006 atomic test, as well as for an unknown number of bombs.

Mr Hill landed in Beijing on Friday afternoon and was due to meet with his six-nation counterparts from China, South Korea and Japan, US embassy spokeswoman Susan Stevenson said.

It was unclear whether North Korean envoy Kim Kye Gwan would come to Beijing for the meetings.

Before leaving for Seoul on Friday, South Korean envoy Kim Sook said the deadlock in the six-nation process needed to be broken quickly.

'It is an important moment in which North Korea should resume the disablement measures,' he said.

The negotiations have suffered countless setbacks and delays, but in a landmark deal signed last year, North Korea agreed to abandon its nuclear weapons in return for economic aid and diplomatic recognition.

In June, the North handed in a long-overdue declaration of its nuclear activities, and blew up the cooling tower at Yongbyon.

In response, the United States eased trade sanctions, but did not take it off its list of state sponsors of terrorism, as stipulated under the deal, because it did not agree on how the declaration could be verified.

Washington has demanded strict inspections of atomic sites, including sampling of materials - something Pyongyang rejects as a violation of its sovereignty.

US White House spokesman Dana Perino said on Thursday that Mr Hill would send a message to Pyongyang that the United States still planned to reward the North if it met conditions agreed to between the six nations. -- AFP