"We perceive it (North Korea) as being a threat in a number of areas to the safety and security of the countries that surround North Korea," the US Federal Bureau of Investigation chief told a news conference after meeting Japanese public security officials.

Washington as well as Japanese and other governments in Asia and the Pacific are "looking at North Korea with a skeptical eye as to our concerns" about the proliferation of weapons of mass destruction, he said.

"We look at North Korea for the potential of participation in criminal activities such as narcotics trafficking. And together we address the threat that currently is North Korea in a number of areas -- proliferation, narcotics trafficking and money laundering."

Asked about a massive explosion which reportedly killed or injured thousands of people at a train station in North Korea, he said he did not have any information to suggest an act of terrorism was responsible for the incident.

"I have not heard myself this time what may have caused that explosion. I heard that there was an explosion," he said.

Mueller arrived here Thursday following an unprecedented three-day visit to China, aimed at expanding anti-terrorism cooperation with Chinese law enforcement agencies.

He said that the US and Japanese authorities had been beefing up a "close working relationship" in the fight against terrorism, organised crime, "cyber-crime" with the use of the Internet and people trafficking.

In a meeting earlier Friday with Kiyoko Ono, who heads Japan's National Public Safety Commission, Mueller thanked Tokyo for its cooperation in global efforts to fight terrorism, Japanese officials said.

Mueller was the first FBI director to visit Japan in four-and-a-half years since Louis Freeh came in 1999.

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