SEOUL (Reuters) - A South Korean intelligence official said on Wednesday that increased activity had been spotted at North Korea’s nuclear reactor, which local media has said could suggest it is being closed down.

A satellite image shows a nuclear facility in Yongbyon, North Korea September 29, 2004. Contrary to published reports, the United States has seen no signs that North Korea has begun to shut down its Yongbyon nuclear facility as called for in a February 13 six-country agreement, a senior U.S, official said on Tuesday. REUTERS/Digital Globe

A U.S. official, however, said that Washington had not seen any sign North Korea had begun mothballing its Yongbyon nuclear plant -- source of weapons-grade plutonium -- as required under a February 13 disarmament agreement.

“We have seen unusual activity around the nuclear reactor so we are currently following and analyzing this,” said a National Intelligence Service official, who asked not to be named.

But he added the government did not conclude that this meant, as some local media reports had suggested, that Pyongyang was taking steps to finally shut down the reactor.

The Dong-A Ilbo daily earlier quoted intelligence sources as saying satellite photographs showed increased vehicle and personnel movements near the secretive state’s reactor site.

The U.S. official, who spoke on condition of anonymity, said news reports in South Korean media are “just not accurate ... We have seen no actions on the North Koreans’ part that at this point leads us to believe they are fulfilling their part of the 60-day actions”.

Under the February 13 agreement reached by the two Koreas, China, Japan, Russia and the United States, Pyongyang had until last Saturday to start the shutdown and invite back U.N. nuclear inspectors.

However, it has refused until it can access funds frozen for more than a year in a Macau bank.

South Korean President Roh Moo-hyun said on Wednesday that the last-minute haggling over when North Korea will start closing the nuclear plant would be resolved.

“There were some unpredictable technical problems that have delayed implementation. Both sides are making efforts and those problems are almost resolved,” Roh told a news conference.

“The delay will not nullify the agreement,” he said.

South Korean officials went to Pyongyang for economic talks with the North, with Seoul indicating it could hold off on sending rice aid to its neighbor that battles chronic food shortages if Pyongyang does not start shutting the reactor.

South Korea cut off its regular food handouts after the North test fired missiles in July. The North stormed out of their last economic meeting shortly after that in anger over the aid cut.