North Korea on Wednesday vowed to strengthen its nuclear arsenal because of the threat from the United States, and never to abandon its deterrent.

The new blow to international efforts to tempt the North back to nuclear disarmament talks was delivered at the UN General Assembly in a rare speech by a North Korean minister on the world stage.

Vice Foreign Minister Pak Kil Yon told the assembly: "As long as the US nuclear aircraft carriers sail around the seas of our country, our nuclear deterrent can never be abandoned, but should be strengthened further. This is the lesson we have drawn.

"The United States is not a defender, but a disruptor of peace," Pak declared.

The minister said North Korea opposes nuclear proliferation but added that without its nuclear bomb, "the Korean peninsula would have been turned into a war field scores of times."

Decades of tensions between North and South Korea have hit a new peak since the sinking of a South Korea navy ship, the Cheonam, in March, killing 46 crew. An international inquiry blamed the North, which has denied involvement.

North Korea is also in the international spotlight with apparent moves to put the youngest son of its ailing leader Kim Jong-Il in position to take over.

Pak accused the Seoul government of "kicking up (a) war atmosphere against their fellow countrymen in collusion with foreign forces."

South Korea and the United States on Monday launched a joint anti-submarine exercise -- the latest in a series since the sinking of the corvette.

The North's minister said: "South Korea is advised not to create tension on the Korean peninsula by waging war exercises with outside forces and pursuing confrontational approach."

He criticized the South for refusing to send an inspection team to the North to see its evidence that it was not involved.

North Korea signed a 2005 commitment to work toward a nuclear-free Korean peninsula, along with the United States, China, Russia, South Korea and Japan. The North withdrew from the talks in 2008. It is under UN sanctions because of its nuclear programme.

China and Russia have indicated they want a quick resumption of the negotiations. The United States and South Korea say they want to see some kind of commitment to success from the isolated North before the talks start again.

"As already clarified, our nuclear weapons are not a means to attack or threaten others, but a self-defensive deterrent, to all intents and purposes, to counter aggression and attack from outside," the minister told the assembly.

"As a responsible nuclear weapon state, we are willing to join in the international efforts for nuclear non-proliferation and safe management of nuclear material on an equal footing with other nuclear weapon states," Pak added.

South Korea's Vice Foreign Miniser Chun Yung-Woo this week accused the North of blocking the six nation talks "to buy time to build up its nuclear capability."

North Korea carried out its first nuclear test in 2006 and a second in May last year.