News reports on Tuesday said that US spy satellite photos indicated that Pyongyang might be preparing to shut down the reactor, days after the communist state missed an agreed disarmament deadline.

"I see nothing... that has either encouraged or discouraged me," in North Korea's actions so far, US Deputy Assistant Secretary of State for East Asian affairs Kathleen Stephens told reporters in Brussels.

"What will encourage me is to see the IAEA (International Atomic Energy Agency) being in touch and getting back into the DPRK (North Korea) and getting on with the work."

US satellites Monday spotted unusual movement of people and vehicles near the cooling tower and parking lot at the Yongbyon facility, which provides plutonium for nuclear weapons, South Korea's Dong-A Ilbo newspaper said.

The United States and South Korea believed it was probably part of operations to close down the reactor, as required under a six-nation disarmament deal reached in February, it said.

The reports raised hopes that Pyongyang might be preparing to take action after an April 14 deadline to close Yongbyon lapsed due to a dispute over millions of dollars frozen in a Macau bank.

Stephens, who was in Brussels for talks with European officials, said there was no new deadline for Pyongyang to fulfil its commitments.

"The time for action is now," she said.

North Korea insists it will begin shutting down and sealing Yongbyon and readmit the UN atomic inspectors once it has retrieved 25 million dollars in funds frozen in Macau's Banco Delta Asia (BDA).

The United States, which orchestrated the freeze on suspicion of money-laundering and counterfeiting, has said the funds were freed for collection at BDA last week.

"I don't think there is any doubt that the accounts are open and available," said Stephens.

She admitted that the bank account issue had been "more complicated and more technical than expected". But she said any remaining problems on Pyongyang accessing the money were between the bank in Macau, part of China, and the account holders.

The United States, China, the two Koreas, Japan and Russia reached a deal in February under which the North should disable its nuclear programmes. In exchange, it would get a million tons of fuel oil or equivalent aid, plus security and diplomatic benefits.

Under the first phase it was supposed by last Saturday to have shut down and sealed Yongbyon, which produces the raw material for plutonium to make bombs, in the presence of UN atomic inspectors.

Stephens said the US was encouraged by a visit by IAEA chief Mohamed ElBaradei to Pyongyang last month and by the creation of a series of international working groups.

"We are seeing a pretty intensive and hopefully intensifying schedule of bilateral consultations as well as multi-lateral consultations," she said.

She hoped it would help move towards the wider goals of a de-nuclearised Korean peninsula and a peace treaty between the two Koreas, she added.