WASHINGTON - Activity at a North Korean facility suggests Pyongyang could be preparing its first test of a nuclear bomb, U.S. media on Thursday cited U.S. officials as saying.

But U.S. officials said they had no new evidence of such a plan, and a diplomatic official in Seoul familiar with the North's nuclear program said he was skeptical of the reports.

North Korean leader Kim Jong-il (2nd L) poses for a picture with the family of farm manager Yun Ho-jung (L) during an inspection of a stock-breeding centre of the Korean People's Army unit 757, in an unspecified location in North Korea, in this undated photo released by Korea News Service in Tokyo August 14, 2006. [Reuters]

ABC News quoted an unidentified senior military official as saying a U.S. intelligence agency had observed "suspicious vehicle movement" at a suspected North Korean test site.

A senior State Department official, who was also not identified, told the network, "It is the view of the intelligence community that a test is a real possibility."

CNN reported U.S. military sources said satellite images had shown wire bundles appearing at a suspected test site that could be used to monitor an underground test. It said the wires had not been connected to anything and that it was still unclear if a test was being prepared.

Asked about the media reports, a senior U.S. official told Reuters, "We have no new evidence to support that." Another official, who also declined to be identified, said there was no indication of a threat in the near term.

State Department spokesman Gonzalo Gallegos declined to comment on intelligence matters.

South Korean government officials had no comment on the report and the diplomatic source in Seoul said he was not aware of a new intelligence report.

"I was not aware of the area mentioned in the report as being a possible site for a North Korean nuclear test," the source said.

ABC said the suspected test site was an underground facility called Pungyee-yok in northeast North Korea. The intelligence was brought to the attention of the White House last week, its report said.

The activity includes the unloading of large reels of cable outside Punggye-yok. Cables can be used in nuclear testing to connect an underground test site to outside observation equipment.

Even before this most recent intelligence, there has been growing concern within the U.S. government that North Korea has been moving toward a nuclear test. North Korea is believed to have enough nuclear material to build as many as a dozen nuclear bombs, but it has never tested one. A successful test would remove any doubt that North Korea is a nuclear power.

"What does he have to lose?" asked one senior military official, referring to North Korean leader Kim Jong Il.

On July 4, North Korea conducted seven ballistic missile tests, which provoked international condemnation, including a unanimous United States Security Council resolution condemning its actions. A nuclear test, however, would be seen as a much greater provocation than the missile tests. Only seven other nations in the world have ever conducted nuclear tests.

U.S. officials fear a nuclear test could provoke a nuclear arms race in East Asia, forcing Japan and South Korea to develop their own nuclear weapons.

"A nuclear test is going to be alarming and troubling for everyone and would cause a very strong reaction I think from all of North Korea's neighbors," said former National Security Council official Michael Green, now with the Center for Strategic and International Studies.

U.S. officials caution that the intelligence is not conclusive. Last year U.S. spy satellites picked up suspicious activity at suspected test sites in North Korea, leading some to predict an imminent nuclear test, but nothing happened.

Officials say it is possible that North Korea may either be putting on a show for American spy satellites to get attention, or may conduct a nuclear test in an entirely different location.

"It is the view of most in the community that there is a 50-50 chance North Korea will conduct a nuclear test by the end of the year," said one analyst.