The delegates said on Saturday they were also permitted to visit the controversial Yongbyon nuclear facility, making them the first outsiders to go there since UN inspectors were expelled a year ago.
"We did go to Yongbyon," said Stanford University scholar John Lewis at Beijing's airport on his return from a five-day trip to North Korea with four other Americans.
The group arrived in Pyongyang on Tuesday with the intention of visiting the Yongbyon facility, where North Korea has said it is reprocessing spent nuclear fuel rods in an effort to make nuclear weapons.
Lewis, who made his "10th or 11th" visit to the reclusive Stalinist country since 1987, said the delegates also wanted to obtain "clarification on critical issues" that have strained ties between the US and North Korea.
The countries have been in a bitter standoff since October 2002 when Washington said Pyongyang had relaunched its nuclear programme in violation of a 1994 bilateral accord freezing the project.
Professor John Lewis found North
Korean officials very cooperative
The US then suspended its delivery of fuel to North Korea, which in turn quit the Non-Proliferation Treaty (NPT) and reactivated its nuclear reactor at Yongbyon, 90km north of Pyongyang.
Pyongyang expelled two inspectors from the UN's International Atomic Energy Agency on 31 December, 2002.
Lewis stressed: "We were there not as officials but as a private delegation. We were not there to negotiate, we were not there to be inspectors."
He and fellow delegate, nuclear scientist Sig Hecker, said North Korean officials had cooperated with the visitors.
"We sent them a list of all our requests and they honoured all of those requests and we made additional ones, they honoured all of those," Lewis said.
Hecker, who from 1985-1997 directed the Los Alamos National Laboratory, where the atomic bomb was first developed, said: "Our hosts in the DPRK (North Korea) were very cooperative, very courteous throughout our entire visit."
Secretary of State Colin Powell
says he is encouraged by events
North Korea offered last week to refrain from producing and testing nuclear weapons in what it said was a "bold concession" to Washington, an offer US Secretary of State Colin Powell said encouraged him.
But Pyongyang vehemently rejected Friday suggestions it follow the example of Libya, which last month said it renounced its quest for chemical, biological and nuclear weapons and welcomed international inspections.
"This is nothing but a folly of imbeciles utterly ignorant of the DPRK's independent policy," Pyongyang's official media quoted a foreign ministry spokesman as saying.
Washington has demanded that Pyongyang unilaterally scrap its nuclear programme, but North Korea has insisted on a legally binding security guarantee from the US in return for a nuclear climbdown.