Olli Heinonen, the International Atomic Energy Agency's deputy director general for safeguards, was due to arrive in Pyongyang Tuesday for a five-day visit, along with three colleagues.

North Korea, which expelled UN inspectors in late 2002, announced last week that it invited a "working-level delegation" to discuss procedures for shutting down the plutonium-producing facility.

"The purpose of this trip is now to go negotiate the details on behalf of the IAEA and verification of the monitoring and closing-down of the Yongbyon facility," Heinonen told reporters at Vienna Airport.

North Korea had pledged in February to shut down the Yongbyon reactor, its main processing facility, and IAEA Chief Mohamed ElBaradei traveled to North Korea in March in what was billed as a landmark visit.

But Pyongyang refused to act on the promise until it received about $25 million in funds that were frozen in a Macau bank amid a dispute with the US over alleged money-laundering.

The funds were freed earlier this year, but only last week started to be transferred to a North Korean account at a Russian bank. Russia said the disputed funds arrived on Saturday.

Heinonen said his delegation's trip was "a subsequent step forward" from ElBaradei's visit.

Asked whether he would visit the Yongbyon facility, Heinonen said, "We will see how the time allows."

Also Saturday, Christopher Hill, the chief US envoy to nuclear talks, said North Korea could shut down its reactor within three weeks and return to international talks next month.