Condoleezza Rice has reaffirmed a US pledge to defend Japan

But he stressed that Japan, the only nation to suffer a nuclear attack, would stick to its policy of not possessing or allowing nuclear weapons.

North Korea's nuclear test on 9 October has triggered fears of a possible arms race in East Asia.

The US has reiterated its commitment to defend Japan in light of the test.

Following talks with Taro Aso in Tokyo, US Secretary of State Condoleezza Rice said the US "has the will and capability to meet the full range... of its deterrent and security commitments to Japan."

It is only in Japan where the discussion about its own nuclear possession is completely absent Taro Aso Japanese Foreign Minister Arms race fears

Mr Aso also confirmed his government has no plans to go nuclear.

"There is no need to have nuclear weapons as the Japan-US security framework will be activated for the defence of Japan," he said.

But earlier, Mr Aso told a parliamentary committee that it was right for Japan to debate the issue.

"When a neighbouring country is going to have nuclear weapons, one can refuse to even consider the matter," he said. "But I think it is important to discuss the issue."

He said the government's position "to stick to its three non-nuclear principles will not change".

"But the issue of nuclear possession has been discussed by many people for decades, and it is only in Japan where the discussion about its own nuclear possession is completely absent," he went on.

Popular support

His comments echo those of a top ruling party official, Shoichi Nakagawa, who said at the weekend that Tokyo should discuss the issue "because countries with nuclear weapons don't get attacked".

Prime Minister Shinzo Abe has this week repeated his assurance that Japan would never go nuclear.

Japan's policy on nuclear weapons stems from WWII, when the US dropped atomic bombs on the cities of Hiroshima and Nagasaki. The policy has long had the popular support of the public.

But if Japan - conceivably most at threat from a nuclear-armed North Korea - ever did decide to obtain nuclear weapons, analysts say South Korea might quickly feel under pressure to follow suit.

This may persuade China, until now the region's only nuclear power, to modernise its own arsenal, potentially triggering a similar response from Taiwan.