Top Japanese officials said the country was preparing for any contingency, although they said there was no specific intelligence pointing to a test this weekend. "We are dealing with the situation with thorough information-gathering and contingency plans, should there be any unforeseeable situation, " defence agency chief Fumio Kyuma told a news conference.

North Korea threatened last Tuesday to conduct a nuclear test to prove it is a nuclear power, although it gave no date.

Caution levels shot up on Friday as a top Japanese diplomat said a test over the weekend was a possibility. "Based on the development so far, it would be best to view that a test is possible this weekend, " Japanese vice-foreign minister Shotaro Yachi told Japanese broadcaster TV Asahi. Yachi was speaking in Washington after a series of talks with US officials on North Korea's latest nuclear threat.

Japan is also pushing the UN Security Council to issue a statement to "transmit a strong united will of the international community" to prevent North Korea from conducting a nuclear test, Shiozaki said.

Media reports have speculated that a test could come as early as today, the anniversary of Korean leader Kim Jong Il's appointment as head of the country's communist party in 1997.

With tensions rising last week, North Korea's leader Kim Jong Il met his top brass and urged them to bolster the nation's defences, North Korea's official Korean Central News Agency (KCNA) said.

Officers greeted him with rousing cheers of "Fight at the cost of our lives!"

North Korean state television aired still shots of the bouffant-haired leader waving to an assembled crowd of about 500 olive-suited officers in dress caps in the capital city, Pyongyang.

It was unclear when the rally took place, or how many had attended, but it could show that Kim is trying to polish his credentials with the country's cherished military at a time when international pressure is mounting on Pyongyang.