There are no signs North Korea has resumed nuclear activity at the site where it previously produced weapons-grade plutonium, a former US envoy was quoted as saying Saturday after a trip to the country.

Charles Pritchard, former top negotiator with North Korea, was quoted as saying that the Yongbyon complex -- where the isolated state processed plutonium for past nuclear tests -- did not appear to be in operation.

"My reaction is that the reactor, the 5-megawatt reactor, remains shut down, the cooling tower is still destroyed," Pritchard told reporters after a five-day trip to North Korea, Japan's Kyodo news agency reported.

"So at this point, I don't believe there is any additional reprocessing or anything going on" at the reactor, the former top US negotiator with Pyongyang said at a Beijing airport, according to Kyodo.

South Korean Defence Minister Kim Tae-Young said in October that Pyongyang was restoring facilities at the Yongbyon nuclear reactor, its source of weapons-grade plutonium in the past.

He added it was "quite possible" that Pyongyang was also enriching uranium for nuclear weapons.

The Chosun Ilbo newspaper in South Korea reported in October, citing unidentified government sources, that North was preparing for a third nuclear test. But US and South Korean officials said there was no evidence of this.

Pyongyang had invited Pritchard, Washington's special envoy to the North under former President George W. Bush, to visit the country, South Korea's Yonhap news agency reported last month, citing a diplomatic source.

Pritchard, who also served as senior director for Asian affairs for former president Bill Clinton, now heads the Washington-based Korea Economic Institute.

Six-party talks aimed to curb the North's nuclear ambitions have been at a standstill since the last meeting in December 2008.

In April 2009 North Korea stormed out of the forum, involving two Koreas, China, Japan, the US and Russia. A month later it conducted its second nuclear test.

The North has recently said it is willing in principle to return to the long-stalled nuclear disarmament talks. But Seoul and the United States say it must first improve cross-border ties and show a commitment to disarmament.