Bush telephoned Japanese Prime Minister Shinzo Abe and South Korean President Roh Moo-hyun and they agreed to work together to ensure North Korea kept its side of the pact adopted at six-nation talks in Beijing this week.

Speaking at a White House press conference, the US leader said the agreement aimed at halting North Korea's nuclear weapons was a "good first step" but added "there is a lot of work to be done to make sure that the commitments made in this agreement become a reality."

Bush defended the deal against critics, including from his key conservative base, who said that offering aid and other guarantees to North Korea in return for disbanding its nuclear network was rewarding "bad behavior" and a sign of US weakness.

Among the agreement's vocal critics was Washington's former envoy to the United Nations, John Bolton, who called it "a very bad deal" that shows US weakness at a time when Washington is challenging Iran over its controversial nuclear program.

It also "undercuts" UN sanctions resolutions against North Korea, Bolton said.

"I strongly disagree, strongly disagree with his assessment," Bush said, however.

The US leader said he wanted to solve the North Korean nuclear crisis peacefully and that he had "an obligation to try all diplomatic means necessary to do so.

"I changed the dynamic on the North Korean issue by convincing other people to be at the table with us on the theory that the best diplomacy is diplomacy in which there is more than one voice that has got an equity in the issue speaking," he explained.

"Now, those who say the North Koreans have got to prove themselves by actually following through in the deal are right, and I'm one," he said.

Under the accord, North Korea will be given 50,000 tonnes of fuel aid for closing their key Yongbyon nuclear facility north of Pyongyang and allowing UN nuclear inspectors back into the country.

The hardline Stalinist state would eventually receive one million tonnes if the accord advances as planned and it permanently disables key facilities.

The United States, for its part, would begin the process of delisting the North as a sponsor of terrorism and normalizing relations with a country with which it is still technically at war, dating back to the 1950s Korean conflict.

Bush on Wednesday telephoned Japanese Prime Minister Abe and South Korean President Roh, who "agreed on the importance of close coordination on North Korea," said US National Security Council spokesman Gordon Johndroe.

Bush said the accord "has provided a way forward for North Korea, but that North Korea must live up to its commitments. The Japanese and South Korean leaders pledged to make sure that North Korea does so," Johndroe added.

Roh's spokesman and a Japanese press agency confirmed that the allies had agreed to keep pressure on Pyongyang to abide by the terms of the agreement unveiled Tuesday.

Bush said China and Russia together with US military allies South Korea and Japan had played a crucial role in moving to end the nuclear crisis afflicting the Korean peninsula.

"Perhaps the most significant voice that had been added to the table was China," he said.

Bush also promised to step up food aid to impoverished North Korea if Kim Jong-Il's regime took "verifiable measures" to end its nuclear weapons program.

On the question of US financial sanctions on North Korea, Bush said it should be treated "separate" from the nuclear weapons issue, even though US chief negotiator Christopher Hill said Monday that Washington intended to resolve the matter within 30 days.

Accusing Pyongyang of money laundering and counterfeiting, the United States imposed the sanctions in 2005, effectively freezing 24 million dollars in North Korean funds in Macau-based Banco Delta Asia.

Meanwhile Russian Foreign Minister Sergei Lavrov told Russian journalists that Moscow plans a "radical reduction" in the debt it is owed by North Korea.

"We are discussing settling the debt," he said. "Conditions can vary but in any event it will be a radical reduction in the North Korean debt.

On Thursday officials from the two Koreas prepared to hold talks aimed at reviving a high-level dialogue and possibly open the way for major aid shipments.

Seoul's delegation, led by Lee Kwan-Se, an assistant unification minister, left for Kaesong early Thursday for the one-day working-level talks, Yonhap news agency reported.

"We hope to make substantive progress not only in a solution to the North's nuclear weapons programme, but also in the government's policy of peace and prosperity by resuming the cabinet-level talks," Unification Minister Lee Jae-Joung told the team.