Top U.S. and North Korean nuclear envoys meet in Singapore on Tuesday to seek a deal in which the secretive North delivers an overdue declaration on its nuclear programmes against a backdrop of stepped-up sabre rattling.

U.S. officials have said they do not expect the actual declaration to come out of the meeting between U.S. Assistant Secretary of State Christopher Hill and North Korea's Kim Kye-gwan, who last met about a month ago in Geneva.

Hill has said time was running out for the North to make the declaration, which it was supposed to deliver at the end of 2007, and answer U.S. suspicions of having a secret programme to enrich uranium for weapons and proliferating nuclear technology and material to the likes of Syria.

North Korea, which has ratcheted up tensions on the heavily armed Korean peninsula in the past few days with missile tests and threats to reduce the South to ashes, said it had already made the declaration and the U.S. suspicions were "fictions".

"Explicitly speaking, the DPRK (North Korea) has never enriched uranium nor rendered nuclear cooperation to any other country. It has never dreamed of such things," its KCNA news agency on March 28 quoted a Foreign Ministry spokesman as saying.

The North's leader, Kim Jong-il, visited military bases, KCNA reported at the weekend, and expressed satisfaction that his soldiers could "beat back the enemy's invasion at a single stroke and firmly defend the socialist homeland".

U.S. officials said they believe North Korea has produced about 50 kg (110 lb) of plutonium, or enough for about eight nuclear bombs. Officials close to the nuclear negotiations said the North may be ready to give an inventory of its plutonium but not much else.

Moon Chung-in, an expert on North Korea at Yonsei University, said perhaps the best that can be expected from the meeting is a commitment from North Korea to return to the nuclear talks with China, Japan, Russia, South Korea and the United States.

If the isolated North makes the declaration, it stands to be removed from a U.S. terrorism blacklist and be better able to tap into international finance that could boost its basket case economy.

Energy-starved North Korea has received heavy fuel oil shipments in return for living up to other parts of the nuclear deal struck in 2005, such as starting to take apart its Soviet-era nuclear plant that makes arms-grade plutonium.

It even kept a date to talk with South Korea about more aid it could receive in the six-way deal, even while threatening to cut off talks with its wealthy neighbour.

Its recent threats are likely aimed at increasing pressure on South Korea's new president to drop his hard line towards it and to secure final concessions from the United States before President George W. Bush leaves office, analysts said.

"North Korea wants to keep things rolling without any meaningful conclusion," said Kim Sung-han, a Korea University professor who specialises in international relations. "This is more beneficial to the regime's survival."