"Some mysterious activity has been continuously detected near the North's suspected nuclear test site but currently there are no signs that could be directly linked to preparations for further nuclear tests," the official told reporters on condition of anonymity.

"In close cooperation with allies, the government has been closely watching any movement that could be linked to a possible nuclear test in the North."

US television network ABC reported Thursday that North Korea appears to have prepared for a repeat test.

Citing US defense officials, it said activity had recently been detected in the same area where the October 9 test took place, Punggye in the northeast.

In the weeks before the first test, US spy satellites detected the unloading of large cables.

"We think they've put everything in place to conduct a test without any notice or warning," a senior US defence official was quoted as saying by ABC News.

The US official cautioned that the intelligence was inconclusive on whether North Korea would go ahead with another test, but said the preparations were similar to steps taken before the first one.

Two other senior defense officials confirmed that recent intelligence suggests the North Koreans appear ready to test a nuclear weapon again, but the intelligence community is divided about whether another test is likely, ABC said.

South Korea's Defence Minister Kim Jang-Soo said last month that North Korea might stage a second test to strengthen its hand during six-party talks on scrapping its nuclear programmes.

The first test on October 9 sparked international condemnation and United Nations sanctions.

Later that month North Korean leader Kim Jong-Il told China that he had no plans for a second test but that increased international pressure could trigger "further measures."

The six-party talks resumed last month after a 13-month break but ended without any apparent agreement and without setting a date for the next meeting.

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