A US envoy left here Thursday for talks in Beijing with his Asian negotiating partners to try to determine whether North Korea had begun to rebuild its nuclear plant, officials said.

The White House and State Department said they hoped that envoy Christopher Hill's meetings on Friday with top diplomats from China, South Korea and Japan would yield clarity about Pyongyang's intentions.

North Korea last week announced that it has stopped work on disabling the Yongbyon nuclear complex, and would consider rebuilding the plants, because Washington has failed to drop it from a terrorism blacklist.

But, seeking to calm matters, US officials said it is too early to tell whether North Korea's activities at the site indicated it was going ahead with re-assembling a plant it started disabling last year under a six-country deal.

"And that's why Ambassador Hill is going to have consultations with ... other parties to the six-party talks to see where we go from here," State Department deputy spokesman Robert Wood told reporters.

The six-party talks involve the United States, China, the two Koreas, Japan and Russia.

"We don't know what to make of it," he said when asked if the movement of equipment meant it was re-assembling the plant. "But, again, we're obviously looking at the situation very closely and will consult with our allies.

Wood said he did not know if North Korea would send an envoy to the talks involving Hill, the assistant secretary of state for Asian affairs, and his counterparts Wu Dawei of China, Kim Sook of South Korea and Akitaka Saiki of Japan.

Traveling with Hill is Sung Kim, the director of the State Department's Korea office, Wood said. Hill is due back in Washington Sunday.

Wood added that North Korean steps "to reverse disablement are obviously of a concern to us" but struck a cautious note by saying Washington still had "no indications that (the North Koreans) are rebuilding" the plant.

Monitors there have been able to "ascertain that some equipment that had been moved to a storage site as part of the disablement process apparently was returned to its previous location," he said.

"But none of that equipment is operational," Wood said.

Analysts and officials in Tokyo said the move could be a pressure tactic rather than a serious attempt to restart the reactor, which is more than 20 years old.

White House spokeswoman Dana Perino said the Beijing meeting was part of efforts to keep North Korea "headed in the right direction," toward eventual dismantlement of its nuclear weapons program.

"We want some clarification on what is happening in North Korea," Perino told reporters, adding that Washington also wants to send a message to the secretive Stalinist regime in Pyongyang.

The United States still plans to reward North Korea once a verification protocol is in place to gauge progress towards the dismantling of North's nuclear facilities under what has been called "action for action," she said.

"And I think that that message will be delivered to the North Koreans," said Perino.

The reactor is at the heart of the North's decades-old nuclear weapons drive and produced the plutonium for its October 2006 atomic test.

"But up and until they move forward on this verification protocol, which is what the six parties agreed to, then we are not going to remove them from the state sponsor of terrorism list," said Perino.