John Bolton, who spoke to a packed audience at the Foreign Correspondents' Club in Hong Kong, said the use of diplomacy by the United States and China was a mistake.

"I think this is a case where you have to acknowledge that North Korea is not really prepared to give up its nuclear weapons programme. Diplomacy is not going to change that outcome," he said.

"(The North Koreans) are experts in selling the same piece of salami over and over again," said Bolton, the US representative to the UN in 2005 and 2006.

"They have successfully for years made commitments, violated the commitments, and yet continued the negotiation, extracting more and more benefits," he said.

Bolton served as Under Secretary of State for Arms Control and International Security from 2001-2005.

The outspoken former diplomat sees China, a major energy supplier to North Korea, as the solution to the problem.

"Pressure from China, cutting off the energy supply, would be the most important thing," he said.

"I think China is concerned that too much pressure will bring the North Korean regime down, and that would lead to a rapid reunification of the Korean peninsula, which China doesn't see in its interest," he said.

"I think that's a mistake on China's part."

Bolton said instability in Northeast Asia would impair China's highest priority of economic development in the region.

Reunification of North and South Korea would eliminate not only the nuclear threat but "the prison camp environment that 20,000 plus North Koreans live in", he said.

The latest round of six-country negotiations -- which include the US, Russia and North Korea itself -- collapsed in Beijing in December last year, leading Washington to halt fuel aid shipments to impoverished Pyongyang.

The leaders of China, Japan and South Korea issued a joint call in the same month for a resumption of diplomacy after the collapse of the talks.

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