"People make plans all the time," spokesman Tony Snow said after Japanese Foreign Minister Taro Aso, in Tokyo, revealed that the aim was "to protect some 20,000 Japanese residents and tens of thousands of tourists" in South Korea.

"It is a standard part of any government's preparation to try to take a look at all alternatives, domestically and internationally, and try to prepare for them," Snow told reporters.

"And in this case, obviously, the United States and Japan, as parties to the six-party talks, have interests in trying to address," he said. "What we're hoping is for the six-party talks to resume soon."

Those negotiations group China, Japan, Russia, North and South Korea and the United States.

Aso, who did not elaborate on the various scenarios being considered, said officials needed to consider "ways to evacuate Japanese nationals using US military vessels and civilian ships."

He added that the plan would also consider how to deal with refugees from the Communist North.

The Asahi Shimbun newspaper reported earlier that Tokyo fears as many as 100,000 to 150,000 North Korean refugees could flood into Japan in the event of an unspecified contingency in the Korean peninsula.

The estimate comes from a committee linked to Japan's national security council, the report said, citing unnamed sources related to the matter.

It said the council concluded that such a large number of refugees would overwhelm existing facilities in Japan and some of them might need to be transferred to a third country.

North Korea shocked Japan and the rest of the world when it announced on October 9 that it had conducted its first nuclear test, sparking international condemnation and UN sanctions on the already impoverished nation.

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