North Korea has secret nuclear sites: UN report

The subterfuge work was probably started in the 1990s without raising suspicions, according to diplomats who have seen the report which could be discussed by a special Security Council sanctions committee in coming days.

The report is based on evidence from US scientist Siegfried Hecker who was taken to a secret site by the North Korean authorities last November.

Hecker has told of seeing hundreds of centrifuges at the Yongbyon complex when he went there. The report quoted him as saying that North Korea must have had foreign help to build the facility, one diplomat, speaking on condition of anonymity, told AFP.

"The report says that the centrifuges at Yongbyon must have been operated at at least one other facility before being moved there," the diplomat added.

"The equipment must have been started at least in the 1990s and had to have been made with outside help," said another diplomat, also speaking on condition of anonymity because the report has not been made public.

The panel of experts were set up to monitor two rounds of sanctions ordered by the UN Security Council against North Korea because of its nuclear bomb program.

"They said that more North Korea entities and individuals should be brought into the sanctions regime," said the diplomat.

The new names who would face a travel ban and assets freeze could be added to the sanctions regime without the need for a new UN Security Council resolution that China would probably oppose.

The United States and other western nations on the 15-member Security Council have already called for tighter sanctions.

The panel met Hecker after his visit to North Korea. None of the experts have been allowed to Yongbyon or any other North Korean facility.

North Korea has already said it has a plutonium bomb. It says it carried out bomb tests in 2006 and 2009.

It admitted that low-enriched uranium was being made at Yongbyon with the centrifuges after Hecker's visit. The North Korean authorities insist the uranium is for a "peaceful" light water reactor.

The UN experts made 10 recommendations, including adding more North Korean nuclear officials and companies to the sanctions list. They said North Korea state entities are using aliases to get equipment and that a wider selection of materials should be put on a list of banned imports, the diplomats said.

Neighboring countries should also tighten export controls to the North, the report was quoted as saying.

North Korea kicked UN nuclear inspectors out of Yongbyon in 2002 before withdrawing from the Non-Proliferation Treaty, the pact banning the spread of nuclear weapons.

The report did not name any country suspected of helping North Korea but the West has accused Iran and North Korea of working together on missile technology.