NATO says the United States has proven that Saudi militant Osama bin Laden and his al-Qaida network are linked to terrorist attacks in New York and Washington. And it says the alliance has determined that the attacks were directed from outside the United States. That means that NATO officially regards the attacks against the United States as attacks against all of the alliance's members.

NATO Secretary-General George Robertson spoke with reporters after the U.S. State Department's top official for counter-terrorism, Frank Taylor, briefed the North Atlantic Council, the alliance's governing body.

Mr. Robertson said the briefing showed that Mr. Bin Laden and his al-Qaida network were involved in the attacks. "The facts are clear and compelling," he said. "The information presented points conclusively to an al-Qaida role in the 11 of September attacks. We know that the individuals who carried out these attacks were part of the worldwide terrorist network, al-Qaida, headed by Osama bin Laden and his key lieutenants and protected by the Taleban."

The secretary general said the information that the attacks originated outside the United States clears the way for the alliance to formally invoke the mutual defense clause in its founding treaty. "On the basis of this briefing, it has now been determined that the attack against the United States of America on the 11th of September was directed from abroad and shall therefore be regarded as an action covered by article five of the Washington Treaty, which states that an armed attack on one or more of the allies in Europe or North America shall be considered as an attack against them all," he said.

This is the first time in NATO's 52 years of existence that the mutual defense clause has been invoked. "I want to reiterate yet again today that the United States of America can rely on the full support of its 18 NATO allies in the campaign against international terrorism," said Mr. Robertson.

But he would not say what precise action the NATO allies are likely to take. He said the United States has still not asked the alliance for any specific action.

NATO officials say they expect any military operation to be a U.S. operation with the participation of some allies, notably Britain, and perhaps France, instead of a NATO operation. The officials say all NATO countries will help in different ways. As one official put it, if some do not become engaged militarily, it does not mean that they are not satisfied with the evidence or do fully support the United States.