PYONGYANG, North Korea -- North Korea moved a step closer to fulfilling a promise to shutter its main nuclear reactor after agreeing with international monitors Friday on how to verify a shutdown.

International Atomic Energy Agency deputy director Olli Heinonen announced the tentative deal after wrapping up a visit this week to the North, which included the U.N. nuclear watchdog's first trip to the Yongbyon reactor since inspectors were expelled from the country in 2002.

"We have concluded this understanding, what our monitoring and verification activities are in principle," Heinonen said from the capital Pyongyang. He did not give details of the agreement.

North Korean state media had no immediate comment.

The news was the latest positive sign in the past several weeks that the North is taking seriously a pledge it made in February to shut down and disable the 5-megawatt reactor, which can produce enough plutonium to churn out one nuclear bomb a year.

The country received a promise of economic aid and political concessions from the United States, China, Japan, Russia and South Korea, its partners in the so-called six-party forum created in 2003.

The accord's initial phase calls for North Korea to shut the Yongbyon reactor and receive 50,000 tons of heavy fuel oil.

Heinonen said his team, set to leave Pyongyang for Beijing today, was preparing to report to the IAEA board of governors within a week.

He said, however, that the agency would have no say in the shutdown's timing.

In Washington, the State Department on Friday welcomed reports on the IAEA visit and said it was awaiting a briefing from U.N. officials.

"We look forward to the early shutdown and seal of the Yongbyon nuclear facility and to implementing all other commitments under the February 13 initial action agreement," said spokeswoman Janelle Hironimus.

An official at the IAEA's Vienna headquarters, speaking on condition of anonymity because he was not authorized to comment to media, said a board meeting would likely take place July 9 with the 35 member nations expected to approve sending the first inspection team to the North as quickly as possible.

Heinonen, who emphasized all week that the trip was not a formal inspection, was upbeat Friday after returning to Pyongyang from an overnight stay at Yongbyon, about 60 miles northeast of the capital.

"We visited all the places which we are planning to visit, and cooperation was excellent," Heinonen said in earlier APTN footage.

He said the facilities remain operational.

Along with the 5-megawatt facility at the Yongbyon Nuclear Center, the officials also saw an unfinished 50-megawatt reactor, the fuel fabrication plant and a reprocessing plant, Heinonen said. He said he thought five facilities at the complex would likely be closed.

Experts said the North was sending the right signals, while not appearing weak.

"North Korea is offering positive signs that it is willing to cooperate once the actual monitoring begins," said Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University.

Paik Hak-soon, a North Korea analyst at the Sejong Institute outside Seoul, said allowing Heinonen's team to travel to Yongbyon was a "well calculated" move.

"The North demonstrated to the international community its will to keep the promise to carry out the shutdown and sealing" of the reactor, he said.

But at the same time it was also a "warning to the United States," he added, that the reactor is still running and the country could produce more plutonium unless Washington keeps its promise to provide economic and political concessions.