Assistant Secretary of State Christopher Hill called the overture "another significant step toward the de-nuclearization" of the Korean peninsula. He said the team of experts would go to North Korea on Tuesday for an initial four-day survey.
Hill said the invitation came out of a U.S.-North Korea meeting last weekend in Geneva. Hill has said at that meeting North Korea agreed to disclose and disable all its nuclear facilities by the end of the year, and he reiterated Saturday that he hoped a full review of the North's facilities would be completed by Dec. 31.
"I think it's a sign that this current phase of disabling is an ambitious phase," Hill told reporters. "We have a lot of work to do. It's a sign of the seriousness of purpose that all parties, including the North Koreans, bring to bear on this issue."
The U.S., Russian and Chinese experts would be the latest to visit since International Atomic Energy Agency officials witnessed the shutdown of North Korea's main nuclear reactor in July.
Under a February agreement with the United States, China, Japan, Russia and South Korea, North Korea agreed to abandon its nuclear programs in exchange for fuel and other foreign aid. The deal came after more than three years of on-again, off-again negotiations during which North Korea successfully detonated a nuclear device.
The three-country team of nuclear experts will discuss with North Korea "the scope and the technical feasibility of specific actions" to disable North Korean nuclear facilities, said Hill, who is accompanying President George W. Bush at a summit of Pacific Rim leaders in Australia.
Their visit will help meet the year-end timeline, Hill said: "Our plan is to get this done by Dec. 31. To do that we need to have some nuclear experts - get some eyes on - and we thought the sooner the better."
Hill said there are many different ways to disable a nuclear facility so that it would be extremely difficult to bring it back on line.
"You can drill a hole in the side of a reactor. You can fill it with cement," he said. "You can do various things, but it helps if you have a site survey and have a look at the reactor first."