Washington: The United States on October 3 played down North Korea's announcement that it has extracted plutonium from 8,000 spent fuel rods and is building more nuclear weapons with it.

"We have seen them make these statements previously," White House Press Secretary Scott McClellan said, adding, "I don't have anything to confirm what they are saying."

"Even if North Korea is not building nuclear weapons, it should not have plutonium. There is no legitimate use for plutonium harvested," he said.

"The US and its allies have warned Pyongyang that it faces deeper isolation unless it dismantles the weapons programme."

Secretary of State Colin Powell said that this was the third time North Korea has announced it is building nuclear weapons.

However, he was willing to give North Korea assurances that it will not invade the country.

While Powell played down the North Korean announcement, Defence Secretary Donald Rumsfeld, one of the moving spirits behind the Iraq invasion, said that people should be concerned by the steady stream of bellicose statements from North Korea.

A top South Korean official said Seoul is investigating the North Korean claim "while keeping all possible options open". The official did not spell out the options.

Earlier in the day, the Korean Central News Agency reported that the reprocessing of some 8,000 spent fuel rods, which had been kept under seal, had been successfully completed by the end of June.

North Korea said it had begun to use the weapons-grade plutonium obtained in the course of reprocessing those spent fuel rods to make atomic bombs.

PTI