The teams -- one of academics and a scientist, the other from Congress -- landed in the Stalinist state from Beijing as Pyongyang offered to refrain from testing and producing nuclear weapons and freeze its nuclear facilities.

"Upon arrival they kept a rather low profile," a Pyongyang-based Western diplomat who met them told AFP. "They arrived here, but were not offered any kind of program or itinerary."

Low level officials from North Korea's Ministry of Foreign Affairs formally greeted them at the airport, he said.

The USA Today newspaper said the group would visit the once-mothballed Yongbyon nuclear power plant where Pyongyang announced in June it was reprocessing spent fuel rods as part of its nuclear weapons program.

One of the groups is led by US congressional staffers Keith Luse and Frank Jannuzi while the other includes former State Department official Jack Pritchard and Sig Hecker, a nuclear scientist who from 1985-1997 directed the Los Alamos National Laboratory where the atomic bomb was first developed.

The two congressional staffers met with US embassy officials during their stopover in Beijing, and would likely be debriefed by US diplomats in either Seoul or Beijing following their scheduled Saturday departure, US officials said.

"It is not unusual for visitors to North Korea to share information and views with the United States following their trips," a US embassy spokesman told AFP. "It would not be surprising if these visitors decided to do the same."

The move appeared to be an about-face by Washington which on Friday disassociated itself from the delegations.

China's foreign ministry wished the delegations well, but said it was not aware of any meetings between the delegates and Chinese officials prior to their departure.

"We hope the visit will contribute to mutual understanding between North Korea and the United States, and in particular that it will help promote dialogue," ministry spokesman Kong Quan said.

Their departure came as North Korea said it would refrain from testing and producing nuclear weapons and freeze nuclear facilities if the US delists it as a country sponsoring terrorism, lifts sanctions and provides economic aid.

The statement on the official Korean Central News Agency and the visits come during an impasse between Pyongyang and Washington on stalled six-party talks seeking to put an end to the North's nuclear ambitions.

The second round of talks that also include China, South Korea, Japan and Russia were scheduled for December. But a timetable for their resumption is now unclear.

North Korea agreed in 1994 to mothball its Yongbyon nuclear complex, 90 kilometres (50 miles) north of Pyongyang, under a nuclear freeze agreement with the United States.

But it fired up the facilities while accusing the administration of US President George W. Bush of seeking to scrap the 1994 accord.

Reprocessing Yongbyon's 8,000 spent fuel rods -- thought to be enough for around six nuclear weapons -- could increase a nuclear stockpile that US intelligence services believes already numbers up to two nuclear devices.

The visit of the delegations is at the invitation of the communist state and an apparent indication that Pyongayang is eager to engage Washington.

If they are allowed to visit Yongbyon, they will be the first American groups to do so since international inspectors were kicked out a year ago.

WAR.WIRE