The United States will not automatically get NATO backing if it seeks to expand its war on terrorism to Iraq, Iran or North Korea, the Western military alliance's chief has said.

NATO invoked Article 5 of its founding treaty after the Sept. 11 terrorist attacks, declaring that these should be treated as an attack on all 19 members of the alliance.

But NATO Secretary-General Lord Robertson said on Thursday the decision was related to the specific attacks on New York and Washington and NATO would have to decide what to do about any new attack -- so Article 5 wouldn't carry over.

"I think if the Americans could produce convincing evidence that there was a link between other countries and the attack that took place, then I think the allies would be seriously interested in that information," he said. "But that hasn't been forthcoming up to this moment."

"So it's a matter for the North Atlantic Council to decide what to do about an attack or any subsequent evidence," Robertson said, referring to NATO's governing body.

In his State of the Union address

on Tuesday, President George W. Bush accused North Korea, Iran and Iraq -- a trio he called an "axis of evil" -- of supporting terrorism. His hard-line stance, especially against North Korea and Iran, raised concerns in Asia and Europe that the US-led war on terrorism would be spread.

The NATO chief said there are threats from countries that now have missiles to deliver weapons of mass destruction. He didn't name any nation.

US National Security Adviser Condoleezza Rice on Thursday called North Korea the world's No. 1 seller of ballistic missiles. The Pentagon accuses the North Koreans of selling missiles to Iran and Pakistan. Iraq has barred UN weapons inspectors for over three years, and is believed to be trying to rebuild its banned weapons programmes.

In a wide-ranging question-and-answer session with journalists at the World Economic Forum, an annual gathering of global leaders in many fields, Robertson said NATO was moving in the direction of dealing with terrorist threats.

This meant the alliance was becoming a forum for intelligence

gathering and sharing, and for bringing together information on nuclear, chemical and biological weapons, he said.

NATO did not directly participate in the US-led campaign that routed the former Taliban rulers from Afghanistan. But Robertson said the United States could not have won the war "without coalition support.”