North Korea nuclear test only a possibility for now

A news report quoted U.S. officials as saying activities at a possible North Korean nuclear site suggested preparations for a nuclear weapons test were under way.

The North defied international warnings and test-launched seven missiles on July 5, including a long-range missile which failed.

"If North Korea conducts a nuclear test, it would be a far more serious situation than the missile tests, something that would shake the foundation of international non-proliferation efforts and pose a very serious threat," Ban said.

But he added much more analysis of the intelligence was needed.

"So far, it is seen as a matter of possibility, and related countries are sharing intelligence and keeping a close eye on the North's activities," he told a news briefing.

North Korea declared in February 2005 that it possessed nuclear weapons but has never proven it by testing one.

U.S. television network ABC news reported a U.S. intelligence agency had observed suspicious vehicle movements at a suspected North Korean nuclear test site. It quoted an unidentified State Department official as saying a test was a real possibility.

Other intelligence and government officials have been skeptical of the report.

Proliferation experts said North Korea has been working for years to develop a nuclear weapon, but no one could say for sure if the North had actually built one.

Six-country talks aimed at ending the North's nuclear weapons program are in deadlock. The last round of the talks took place in November.

Japan's top nuclear envoy Kenichiro Sasae arrived later and was scheduled to hold talks with South Korea's nuclear negotiator Chun Yung-woo and a senior presidential Blue House official, an official said.

Separately, Song Min-soon, South Korea's chief presidential secretary on national security, will visit China for two days on Thursday and meet with Foreign Minister Li Zhaoxing to discuss the North's nuclear and missile programs, the presidential office said.