North Korea has offered to fully declare all nuclear weapons programs and disable them by the end of the year, meeting U.S. hopes for quick moves following the shutdown of Pyongyang's sole operating reactor, South Korea's envoy said Wednesday.

"North Korea expressed its intention to declare and disable (all its nuclear facilities) within the shortest possible period, even within five or six months, or by the end of the year," Chun Yung-woo said.

He said North Korean negotiator Kim Kye Gwan also told South Korea at six-nation talks his country was "willing to declare all its nuclear programs without omitting a single one."

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The pledge for total disclosure is key because it implies the North will also include a mention of the uranium enrichment program that it has never publicly acknowledged. The U.S. accused Pyongyang in 2002 of embarking on such a program in violation of an earlier disarmament deal — sparking the latest nuclear crisis.

The arms talks — which include China, Japan, Russia, the U.S. and the two Koreas — began Wednesday with an infusion of optimism after North Korea shut down its reactor Saturday.

The atmosphere of the talks was "as bright as Beijing's skies and was more serious and businesslike than any other time," Chun said Wednesday after a meeting of all six countries at a Chinese guesthouse as the capital was bathed in sunshine.

Japan also said it was impressed by North Korea's positive attitude.

"I had the impression that North Korea is prepared to implement the initial stage steps," Tokyo's envoy Kenichiro Sasae said, referring to the list and disablement.

Chun said the North's declaration should also include bombs the North has built.

"If North Korea has something, whether it be a nuclear weapon or a nuclear detonation device, it should declare all of them," he said.

Earlier Wednesday, the U.N. nuclear watchdog confirmed that North Korea shuttered all remaining facilities at its main nuclear complex in addition to its only working reactor.

"We have verified all the five nuclear facilities have been shut down," Mohamed ElBaradei, chief of the International Atomic Energy Agency, told reporters during a visit to Kuala Lumpur, Malaysia.

Some of the facilities have also been sealed by U.N. inspectors, ElBaradei said.

ElBaradei announced earlier in the week that inspectors had verified the shutdown of North Korea's only working nuclear reactor at Yongbyon, 100 kilometers (60 miles) north of Pyongyang.

His announcement Wednesday confirmed four additional facilities were also shuttered, including two long-dormant construction sites for larger reactors, and facilities for making reactor fuel and reprocessing it to harvest plutonium for bombs.

ElBaradei said having the facilities listed and dismantled by year-end could only happen if there was progress in the six-nation talks and the North remains cooperative with inspectors, who may be required to travel across the secretive nation to other sites.

"What is really important is full transparency," ElBaradei said. "The more transparency we get, the quicker we will be able to verify that everything in (North Korea) has been declared to us."

North Korea has begun receiving 50,000 tons of oil from South Korea as a reward for the reactor shutdown, and is to eventually receive the equivalent of a total 1 million tons for disabling its nuclear facilities.

But Pyongyang has also demanded the U.S. and Japan end their "hostile" policies against the regime, such as other economic sanctions and being named on a U.S. list of terrorism-sponsoring states.

The countries involved in the arms talks last met in March, although the main U.S. envoy Christopher Hill made a surprise trip to Pyongyang in June — his first ever — to urge the North to comply with its pledges.

Complete coverage is available in FOXNews.com's North Korea Center.