The US military Tuesday vehemently denied a media report that special forces had been parachuted into North Korea on intelligence-gathering missions, saying a source had been misquoted.

Current affairs magazine The Diplomat quoted Brigadier General Neil Tolley, commander of special forces in South Korea, as saying soldiers from the U.S. and South Korea had been dropped across the border for "special reconnaissance" missions.

A senior U.S. official warned North Korea Monday against conducting another nuclear test, saying it would be a "serious mistake" that would incur more sanctions and further isolation.

"I think it will be a serious miscalculation and mistake if North Korea were to engage in a nuclear test," Glyn Davies, U.S. special envoy for North Korea policy, told reporters.

Twenty-nine Chinese fishermen have been kidnapped at sea by unidentified North Koreans who have demanded 1.2 million yuan ($190,000) in ransom, fellow sailors and media said Thursday.

The men were fishing in three separate vessels on May 8 when a group of gunmen boarded their boats and forcibly took them over, locking up those on board, said a boat owner surnamed Sun who has been in touch with them.

South Korea, the United States and Japan will hold high-level talks in Seoul next week about developments in North Korea following its failed long-range rocket launch, a report said Thursday.

Lim Sung-Nam, South Korea's chief nuclear envoy, his Japanese counterpart Shinsuke Sugiyama and the U.S. special envoy on the North Glyn Davies will meet on Monday, Yonhap news agency quoted a foreign ministry official as saying.

China, Japan and South Korea said a fresh nuclear test by North Korea would be unacceptable, according to South Korean President Lee Myung-Bak on Sunday.

"Our three countries agreed that we will not accept further nuclear tests or further provocations from North Korea," Lee told reporters after a meeting in Beijing.

North Korea said Thursday it would strengthen its nuclear deterrent and other defenses regardless of cost, amid fears it is preparing for another atomic weapons test.

"No matter what high expense the army and people of the DPRK (North Korea) have to cover, they will further bolster its defense capability including nuclear deterrence to firmly protect its dignity and sovereignty," said a state body known as the Committee for the Peaceful Reunification of Korea.

A Cuban government delegation has arrived in South Korea for the first time in more than half a century, officials said Tuesday, as the communist island moves towards a market economy.

The four-member group were the first Cuban government representatives to visit the capitalist South since Seoul cut ties with Havana after the 1959 Cuban revolution, said Seoul's foreign ministry.

The U.N. Security Council on Wednesday ordered sanctions against three "very significant" North Korean state firms over the country's failed rocket launch, U.S. ambassador Susan Rice said.

With fears mounting that North Korea is about to stage a nuclear bomb test, the United States, European Union, South Korea and Japan had proposed a list of 40 companies, organizations and individuals.

North Korea has apparently finished preparations for a third nuclear test and is awaiting a political decision to go ahead with it, a nuclear expert with South Korea's government said Wednesday.

The expert also said the communist state is likely to use highly enriched uranium (HEU) for any test, and may have produced enough HEU to make between three and six bombs in addition to its plutonium stockpile.

The United States, South Korea, Japan and European countries have proposed dozens of North Korean firms and entities be added to a U.N. sanctions list over the isolated state's rocket launch, diplomats said Tuesday.

But with fears growing that North Korea is now about to stage a nuclear weapon test, the deadline for agreeing to new sanctions may be put back because China, the North's closest ally, has not yet agreed to the measures, diplomats said.