The main U.S. envoy on the issue, meanwhile, said that the United States is looking to build on momentum and will start deliberations on removing North Korea from a list of terrorism-sponsoring states.
North Korea pledged in an international accord in February to shut the reactor at Yongbyon and dismantle its nuclear programs in return for 1 million tons of oil and political concessions. However, it stalled for several months because of a separate, but now-resolved dispute with the U.S. over frozen bank funds.
The shutdown over the weekend was confirmed by a 10-member team of IAEA inspectors, said Mohamed ElBaradei, chief of the International Atomic Energy Agency. "The process has been going quite well and we have had good cooperation from North Korea. It's a good step in the right direction," ElBaradei said, speaking in Bangkok ahead of an event sponsored by Thailand's Science Ministry.
The Yongbyon reactor, about 60 miles north of the capital, generates plutonium for atomic bombs; North Korea conducted its first nuclear test explosion in October.
On Monday, South Korea sent the second of two initial shipments of what eventually will be 50,000 tons of oil to reward North Korea specifically for the reactor shutdown. The first arrived Saturday, prompting North Korea to begin the shutdown of the Yongbyon. The second shipment departed Monday, South Korea's Unification Minister Lee Jae-joung said.
The North's Foreign Ministry said Sunday that further progress under the disarmament accord would now depend "on what practical measures the U.S. and Japan, in particular, will take to roll back their hostile policies toward" North Korea.
In an interview with The Associated Press, U.S. nuclear envoy Christopher Hill laid out an aggressive agenda of a steps Washington hopes can be made in the reconciliation process as Pyongyang lays aside its nuclear weapons program.
"If North Korea wants to denuclearize, all of this stuff is very doable," Hill told the AP.
A first step will be the North declaring a complete list of its nuclear programs to be dismantled. However, the North has yet to publicly admit to embarking on a uranium enrichment program _ which the U.S. in 2002 alleged it had done to spark the nuclear crisis. Washington wants the facilities disabled by the end of the year so they cannot be easily restarted, Hill said.
Along with the oil deliveries, Hill said the U.S. would look at other incentives for the North such as humanitarian aid.