The United States will shortly send Christopher Hill, the assistant secretary of state for East Asian and Pacific affairs, to South Korea, Japan and China for talks to cope with the new development in the nuclear stand-off, the Japanese newspaper Asahi Shimbun said.

Washington has verified that operations at the five-megawatt reactor in Yongbyon were suspended in April, the influential daily said in a report from Washington quoting sources including US government officials.

The US administration reached the conclusion by analysing satellite pictures and estimating temperatures on the walls of nuclear facilities and amounts of steam coming from boilers at Yongbyon, north of Pyongyang, the report said.

Pyongyang could double its nuclear arsenal if it reprocesses 8,000 spent nuclear rods from the Yongbyon reactor as it has claimed to have done before.

The controversial reactor was frozen under a 1994 deal with a US-led consortium which promised to provide the Stalinist state with reactors which produce much less weapons-grade plutonium and heavy oil.

But the North reactivated the reactor in late 2002 after Washington accused Pyongyang of going ahead with a separate, secret nuclear weapons programme based on highly enriched uranium.

The new nuclear stand-off has led to six-nation talks involving the two Koreas, China, Russia, the United States and Japan to end the North's nuclear arms ambitions.

Pyongyang has suspended the negotiations, accusing the United States of hostility, and in February declared that it possessed nuclear weapons for self-defense.

Selig Harrison, a senior researcher at the US Center for International Policy, said after visiting Pyongyang earlier this month that North Korean officials suggested they would start reprocessing the spent fuel rods in late April unless the United States promised not to try to topple the regime of Kim Jong-Il.