PANMUNJOM, Korea — North Korea said today it was preparing to restart its nuclear reactor, accusing America of failing to fulfill its obligations under an international disarmament-for-aid agreement.

It was the first time the North has confirmed it has begun reversing what it has done so far to roll back its nuclear program, though it has warned it would do so in anger over Washington’s failure to remove it from the U.S. terrorism blacklist.

“We are making thorough preparations for restoration” of the Yongbyon nuclear complex, the deputy director-general of North Korea’s Ministry of Foreign Affairs, Hyun Hak Bong, told reporters. He did not say when Yongbyon might begin operating again.

Mr. Hyun spoke to reporters in the border village of Panmunjom before sitting down for talks today with South Korean officials on sending energy aid to the North as part of the six-nation disarmament deal.

Under the landmark 2007 pact — involving the two Koreas, the U.S., China, Russia and Japan — North Korea pledged to disable its nuclear program in a step toward its eventual dismantlement in exchange for diplomatic concessions and energy aid equivalent to 1 million tons of oil.

North Korea began disabling the Yongbyon complex last year, and the process was 90% complete, with eight of 11 key steps carried out “perfectly and flawlessly,” Mr. Hyun said.

Major progress was made in the agreement in late June when North Korea submitted a long-delayed declaration of its nuclear activities and destroyed the cooling tower at Yongbyon in a show of its commitment to denuclearization.

But the accord ran aground in mid-August when Washington refused to take North Korea off its list of states that sponsor terrorism until the North accepts a plan to verify its nuclear declaration.

North Korea responded by halting the disabling process and is now “proceeding with work to restore (Yongbyon) to its original status,” Mr. Hyun told reporters.

South Korean and American officials have said it would take at least a year for North Korea to restart the reactor if it is completely disabled.

Mr. Hyun warned Washington not to press the verification issue, saying verification was never part of the deal.

“The U.S. is insisting that we accept unilateral demands that had not been agreed upon,” he said. Mr. Hyun said forcing North Korea to comply with such an inspection would exacerbate tensions.

The White House had no immediate reaction early today.

The six-nation talks last convened in July, and a new round has not been scheduled because of the current standoff between the U.S. and North Korea.

However, the talks today between the two Koreas — which were proposed by the North — indicate it does not want to completely scuttle the six-party negotiations, analysts said.

“The North is sending a message that it wants to maintain the six-party talks,” a North Korea expert at Seoul’s Dongguk University, Koh Yu-hwan, said. “The North also wants to get the remaining energy aid with winter drawing closer.”

Seoul’s delegate, Hwang Joon-kook, assured North Korea that it would receive the remaining energy aid it was promised.

South Korea’s foreign minister said North Korea’s intentions remained unclear.

“It’s still uncertain whether the North’s measures are aimed at reversing the whole situation to the pre-disablement level” or are a negotiating tactic, Yu Myung-hwan told reporters.

The tensions come amid reports that North Korean leader Kim Jong Il has suffered a stroke. Kim, 66, has not been seen in public for more than a month and has missed two major public events: a military parade marking North Korea’s 60th birthday and the Korean Thanksgiving holiday.

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Associated Press writer Jae-soon Chang in Seoul contributed to this report.