The head of the United Nations nuclear agency, Mohamed ElBaradei, says his inspectors have confirmed that North Korea has shut down its nuclear reactor at Yongbyon, a key step in efforts to halt the country's production of nuclear weapons. From Bangkok, Roger Wilkison reports ElBaradei says North Korea's move is positive but that there is still a long way to go before its nuclear arsenal is dismantled.

IAEA head Mohamed ElBaradei talks to members of the media during the meeting on science and technology assembly in Bangkok, Thailand, 16 July 2007

"Yes, the Yongbyon reactor has been shut down. We have verified the shutdown of the reactor," he said. "We are going through verifying the shutdown of the other five facilities and by tomorrow, after tomorrow, we will be able to report that all the five facilities have been shut down."

ElBaradei says it will take his inspectors, who arrived in North Korea on Saturday, about a month to install seals and monitoring equipment to make sure Pyongyang keeps the reactor closed.

North Korea said on Sunday it had shut down its plutonium-producing reactor, about the time it received a shipment of oil from South Korea as part of February's aid-for-disarmament agreement.

Seoul says it sent a second shipment of oil to the impoverished North on Monday.

Six-party talks to map out the next phase of Pyongyang's disarmament begin in Beijing on Wednesday.

ElBaradei says that the shutdown of Yongbyon is only an initial step.

Referring to North Korea by its official name, the Democratic People's Republic of Korea, or DPRK, he says it now has to provide a complete list of its nuclear arms facilities.

"Well, the next step, obviously, will be through the six-party talks to agree on how to disable these facilities when the DPRK will come with an inventory of all its nuclear materials and facilities," he said. "That, obviously, will take some time. It's a complicated process."

The United States says North Korea has a secret program to make bombs out of highly enriched uranium. Pyongyang has never publicly acknowledged having that program, but the other countries in the six-party talks say it must be declared as part of the nuclear disarmament deal.

Speaking to reporters in Seoul, the chief U.S. negotiator at the talks, Assistant Secretary of State Christopher Hill, also called on Pyongyang to fully declare its nuclear assets.

"We will work on looking ahead to how we are going to get to the full declaration. The full declaration needs to be full," he said. "We need to look at all aspects of denuclearization. So we'll see. We're taking this step by step."

Hill says he expects the negotiations with North Korea to be long and difficult.