Rep. Curt Weldon, R-Pa., who led a congressional delegation that visited Pyongyang for three days ending Sunday, said North Korean officials also told them they had almost completed reprocessing 8,000 spent fuel rods.
"They admitted to having nuclear capability and weapons at this moment," Weldon said at a news conference in Seoul. "They admitted to an effort to expand their nuclear production program."
Weldon's comments echoed those of U.S. officials following talks in Beijing in April. They said that North Korea claimed during a pause in the formal talks that it already had nuclear weapons, but would give up the program in return for economic aid and security guarantees.
On Monday, Deputy Defense Secretary Paul Wolfowitz said the North's nuclear claims shouldn't be ignored.
"Certainly what we know suggests that we should take what they (North Korean officials) are saying very seriously," he said at a news conference in Seoul.
Weldon said at a separate news conference in Seoul that North Korean Vice Foreign Minister Kim Kye Gwan repeated the nuclear claim during a dinner meeting. Both Kim and Foreign Minister Paek Nam Sun told Weldon that Pyongyang planned to produce more nuclear weapons and had nearly finished reprocessing the spent nuclear fuel rods needed to do so, despite pressure from the United States and its allies.
"They admitted to having just about completed the reprocessing of 8,000 rods," said Weldon, who is the No. 2 member of a U.S. House panel that oversees the armed forces.
U.S. experts say that reprocessing the rods could give North Korea several more nuclear bombs within months.
Although they were not traveling as envoys of President Bush, they were the first American officials to visit since the nuclear standoff began in October. They flew to Seoul on Sunday to brief South Korean officials on their Northern trip.
North Korea said it was developing its nuclear weapons as "a response to what they saw happened in Iraq, with the U.S. removing Saddam Hussein from power," Weldon said.
North Korea has previously argued that it is seeking nuclear arms in order to counter what it perceives as a threat from the United States, manifested in the Bush administration considering North Korea a member of the "axis of evil" and the new U.S. policy of preemptive warfare.
A North Korean foreign ministry spokesman was quoted as saying by state-run KCNA news agency that the visit helped both sides better understand each other and they shared the view that Washington and Pyongyang needed to avoid confrontation and exist peacefully.
"They were of the same view that it is necessary to seek a negotiated settlement of the nuclear issue and expressed their stand that it is necessary to continue seeking and discussing ways of settling it," the spokesman said.
In Seoul, South Korean President Roh Moo-hyun said his government has no "clear proof" to conclude North Korea has nuclear weapons.
U.S. and South Korean officials say that North Korea may be bluffing about its nuclear program in an attempt to extract concessions from the United States.
Wolfowitz said Saturday in Singapore that Washington hoped putting pressure on North Korea's battered economy would resolve the nuclear standoff. On Monday, Wolfowitz stressed that military readiness was just as important.
In meetings with South Korean officials, Wolfowitz urged them to increase military spending on new technologies and telecommunications equipment.
"They still work with paper and pencil instead of with the kind of modern communications gear that our special forces took with them to Afghanistan," Wolfowitz said.
The nuclear crisis flared last October when U.S. officials said North Korea admitted running a secret nuclear weapons program in violation of a 1994 accord.
That prompted the U.S. to stop fuel shipments that were allowed under the deal.
North Korea claimed that the U.S. had already violated the 1994 deal by withholding official recognition of North Korea and failing to build civilian nuclear power plants in a timely fashion.
When the U.S. and allies cut off fuel supplies, North Korea kicked out international nuclear inspectors.
Since the beginning of the recent dispute, the U.S. has supported multilateral talks, while Pyongyang has insisted on one-on-one negotiations with Washington.
In a possible victory for the United States, a senior administration officials told The New York Times that China may have convinced North Korea to allow talks involving South Korea and Japan.