"So far the visit has been good, but beyond that I'm not going to comment," US congressional staffer Frank Jannuzi told AFP from his Pyongyang hotel.

Other delegation members also refused to comment.

The delegation arrived in Pyongyang on Tuesday with the intention of visiting the Yongbyon facility where North Korea has said it was reprocessing spent nuclear fuel rods in an effort to make atomic bombs.

Jannuzi was travelling with his colleague Keith Luse. Both work for the US Senate Relations Committee.

The second delegation is led by Stanford University scholar John Lewis and 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.

They will return to Beijing Saturday, Jannuzi confirmed.

Western diplomats in Pyongyang told AFP the teams had kept a low profile in the Stalinist nation. They said the delegations had been "in the field" Thursday.

The visit comes with the second round of six-party talks over North Korea's nuclear ambitions stalled over differences between Washington and Pyongyang over a reported plan to freeze the North's nuclear facilities in return for economic and energy aid.

China, South Korea, Japan and Russia round out the other four parties in the talks.

Washington wants a multilateral system to verify the end of North Korea's nuclear programme in place before aid and energy supplies are granted, while North Korea is calling for a simultaneous step-by-step deal, reports have said.

As the two non-governmental delegations departed from Beijing on Tuesday, North Korea offered to refrain from testing and producing nuclear weapons in what it said was a "bold concession" to the United States.

US Secretary of State Colin Powell said he was encouraged by the offer.

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 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.

WAR.WIRE