A new warning of possible terror attacks against the United States or American targets within the next week was issued last night by the FBI, which said the alert was based on "credible information".
The warning, the second since the 11 September attacks, came on the eve of a new campaign by Tony Blair today to shore up public support for the Allied war in Afghanistan.
The US Attorney General, John Ashcroft, said: "The administration has concluded, based on information developed, that there may be additional terrorist attacks within the United States and against United States' interests over the next week."
The FBI director, Robert Mueller, said the information was "not specific as to intended target or as to intended method", and emphasised that the earlier warning, issued on 11 October, may have helped avert an attack.
Amid the heightened alert, Mr Blair, in a speech in Wales, will seek to prevent a haemorrhaging of support for the military operation by urging people to think back to the atrocities in New York and Washington on 11 September.
His message will also be directed at Muslim countries hoping to see a quick end to military action in the region.
Although ministers insisted yesterday that the British public still had the "stomach" for a long battle, they were worried support might wane if there were no early breakthroughs. There has been frustration in the Government at criticism in the media over the apparent lack of progress in Afghanistan.
President George Bush warned last night that patience would be needed. "It's going to take a while to achieve our objective," he said.
Mr Blair will say: "Never forget how we felt watching the planes flying into the Trade towers. Never forget those answerphone messages. Never forget how we felt imagining how mothers told their children they were about to die. Never forget the guts of the firefighters and police who died trying to save others."
Mr Blair will encourage people to remember the "ghastly menace" of Mr bin Laden's videos, and the long list of countries that lost sons and daughters. "It is not us who is at war with Islam. It is al-Qa'ida and the Taliban who are war with anyone, whatever their faith, who does not share their maniacal and fanatical view of the world," he will say.
The Prime Minister's official spokesman said that in the Kosovo war there were warnings that air power alone would not succeed and that ground troops would fail. "Milosevic is in court, the refugees went home and the doom merchants were proved wrong," he said.
However, the military operation was questioned further yesterday, when Rear Admiral James Burnell-Nugent, commander of the UK Amphibious Task Group, the officer in charge of the British task force being sent to fight, admitted he had no clear idea how the campaign would be conducted. He said: "I don't think it's clear in anyone's mind. That is the challenge. We are in the business of asymmetric warfare."
British commandos are due for a 10-day holiday after a month in the desert, he added, and might not be ready for operations until the Muslim month of Ramadan is about to begin.
But the US Secretary of Defence, Donald Rumsfeld, and his British counterpart, Geoff Hoon, dismissed calls for a halt to the bombing for Ramadan, starting on 17 November.
As warplanes mounted heavy attacks yesterday on suspected hiding places of Mr bin Laden, the US armed forces considered setting up a ground base in northern Afghanistan for commando operations.Reuse content