British Foreign Secretary Mr Jack Straw has warned the world faces potentially the most dangerous situation since the Cuban missile crisis of the 1960s.
Mr Straw also said for the first time that Britain's own intelligence assessment points at Saudi exile Osama bin Laden for last week's New York and Washington attacks.
"One thing is now clear," he told BBC Radio. "I say that this is now clear not only from what has been said in the United States but from our own separate intelligence assessment - Osama bin Laden and his organisation are plainly the prime suspects for this terrorist outrage.
"They do have to be stopped from further such outrages, which for certain would go on if they were not stopped".
But Mr Straw said there were huge difficulties in defeating fanaticism. "We face in individuals like Osama bin Laden, and the organisation which he has, people who do not subscribe to even the most basic moral tenets that the rest of us subscribe to".
He said the world faced a deadly threat from "people who are willing to use aircraft with innocent passengers on board as Cruise missiles".
Mr Straw also thanked Pakistan's president, Mr Pervez Musharraf, for the stand he has taken.
Pakistan has said it would offer the United States full cooperation but that any decision on specific help for its coalition would be taken once Washington makes known precisely what action it has in mind.