It was not immediately clear whether it was posturing or represented Pyongyang's official line as the remarks were not made by North Korea's chief negotiator, Vice Foreign Minister Kim Yong-il.
"There's no need to hold this kind of talks," the delegate, whose identity was unknown, told reporters on Saturday before departing the Chinese capital after three days of discussions with the United States, South Korea, Russia, Japan and host China.
"We're no longer interested. Our expectations have diminished," the delegate said.
"We have concluded that the United States has no intention to switch policy but is trying to disarm by using tricks," he said. "Since it has become clear that the United States just wants to disarm us, we have no other choice."
The talks in Beijing ended on Friday with no major breakthrough, but the six nations agreed to meet again within two months. No place or date was set.
Japan's Kyodo news agency quoted sources with connections to North Korea as saying the statement by the North Korean delegate should not be interpreted too literally.
Asked if the delegate's statements meant North Korea would not take part in future conferences, the source was quoted as saying: "It didn't refer to the issue of the next round of talks. It would be better not to blow it out of proportion."
Pyongyang took a parting swipe at the United States on Friday, likening Washington to a "brigand" determined to disarm and then invade North Korea.
The Bush administration says it is committed to a peaceful resolution, but hawks in the United States are convinced North Korea has nuclear weapons.
Washington has branded reclusive Pyongyang part of an "axis of evil" along with pre-war Iraq and Iran.
The administration says it is committed to a peaceful resolution, but hawks in the United States are convinced North Korea has nuclear weapons.
Earlier on Saturday, US Assistant Secretary of State James Kelly said the talks were productive but there was a long way to go before the crisis was defused.
"We had a nice visit and a productive start. We have a long way to travel and don't know when we will be back here or whether it will be somewhere else," Kelly told reporters before departing Beijing. "But a peaceful solution is something we are going to work on."
South Korea's national security chief Ra Jong-yil was upbeat.
"We could expect the outlook for the next round of talks to be positive," Ra told domestic SBS radio. "I'm confident about it."
Ra brushed off foreign media reports over North Korea declaring it possessed nuclear weapons. "That's just a repeat of its stance that it has no other choice but to go nuclear in case of no security guarantee," he said.
"That's not revealing its will to carry out a nuclear test."
US officials have said North Korea raised the rhetoric on Thursday by talking about carrying out a test and saying it could declare itself a nuclear power.