SEOUL, South Korea - A shipment of oil headed Thursday to North Korea in exchange for the expected shutdown soon of the communist nation's only working nuclear reactor, which would be the first step by Pyongyang to stop making atomic bombs in nearly five years.

The chief UN inspector, Mohamed ElBaradei, said he expects the agency's monitoring of the shutdown of the North's Yongbyon reactor will start "early next week" and the initial inspection is expected to be completed "within a maybe month or so."

"I expect that operation to move smoothly," ElBaradei, head of the International Atomic Energy Agency, said in Seoul of the visit by inspectors to North Korea expected to begin Saturday. "I am quite optimistic that this is a good step in the right direction."

A South Korean ship -- the 6,750-ton No. 9 Han Chang -- departed for North Korea from the port of Ulsan on South Korea's southeast coast, carrying an initial batch of 6,200 tons of heavy fuel oil being given to the North for its agreement to shut down Yongbyon.

The ship was expected to arrive Saturday in the North's northeastern port of Sonbong and will take some 48 hours to unload.

North Korea, after refusing to go forward with the accord for months due to a banking dispute with the U.S. government, strongly hinted last week that it would undertake the long-delayed shutdown as soon as it receives an initial shipment of oil aid.

The shipment is part of 50,000 tons promised for the reactor shutdown, and the North would get an additional 950,000 tons of energy aid if it disables all its nuclear facilities under a February deal with the U.S., China, Japan, Russia and South Korea.

If the North shuts down Yongbyon, it would be the first move it has made to scale back its atomic weapons development since the nuclear standoff began in late 2002. In the first months of the crisis, Pyongyang kicked out U.N. monitors and restarted Yongbyon.

Tensions in the standoff climaxed with the North's first-ever nuclear test in October last year.

ElBaradei said that beyond these initial moves, the North's eventual entire abandonment of its nuclear facilities would be a "long process" that would depend on progress at the six-nation disarmament talks.

"We should not delude ourselves," said ElBaradei, who was attending an international atomic technology conference in Seoul. "It will take time to have a comprehensive solution."

On Wednesday, he had said it was unclear when the North would actually switch off the reactor.

China's Foreign Ministry said Thursday that international talks on dismantling North Korea's nuclear bomb program will resume next week. Spokesman Qin Gang announced at a regular news conference that the talks would be held July 18-19 in Beijing. The negotiations were last held in March.

North Korea had refused to honor the shutdown pledge because of a banking dispute with the U.S. surrounding North Korean funds frozen in a Macau bank blacklisted by Washington over accusations of money laundering and counterfeiting. The financial dispute was resolved recently as the U.S. helped release the funds.