US Secretary of State Colin Powell earlier warned that the "considerable" military buildup surrounding the central Asian nation could lead to the downfall of the Taleban.
"[Bush] Administration policy is to go after the al Qaeda network and Osama bin Laden in Afghanistan and if the Taleban does not realise that this ... might lead to their demise, they will soon come to that conclusion," General Powell said.
The US fuelled speculation that military strikes were imminent by sending classified cables to foreign Governments outlining its evidence that al Qaeda was behind the September 11 attacks that killed nearly 6000 in New York and Washington.
The Guardian newspaper in London said last night that bin Laden was seen in Kabul last week and US and British intelligence sources had a "pretty good idea" where he was.
The US military has kept a tight veil over its plans to punish those responsible. But there was no hiding the departure from Japan of the aircraft carrier Kitty Hawk, with few of its strike planes on board.
A Pentagon source said the Kitty Hawk could serve as a "lily pad" in the Indian Ocean for raids by special operations helicopters and troops.
The ship steamed out of port near Tokyo to join three other aircraft carriers, carrying more than 200 warplanes, already within striking distance of Afghanistan. Another 300 aircraft are positioned in Turkey, Saudi Arabia and Diego Garcia.
The US and Britain have 41 warships equipped with missiles and attack helicopters in the Persian Gulf and the Sea of Oman.
Kazakhstan has offered the use of its air and military bases, likely to serve as launch points for special forces raids.
Uzbekistan, which borders Afghanistan and has the most sophisticated airfields in Central Asia, agreed on Monday to open its airspace to US operations.
But the regime remains defiant. Taleban Defence Minister Mullah Obaidullah urged 15,000 troops gathered on the Pakistan border to resist any attack on Afghanistan.
One thing that may hold up a strike, say defence planners, is the unfolding refugee and humanitarian crisis inside the country.
The first UN food convoy since the terrorist attacks reached Kabul yesterday, carrying 218 tonnes of wheat.
Emboldened by the pressure on their puritanical rulers, Afghan opposition groups are pressing for a Loya Jirga, or grand council of elders and spiritual leaders, to succeed the Government.
Exiled King Mohammad Zahir Shah has announced a pact with the opposition Northern Alliance, clearing the way for a moderate post-Taleban future.
Taleban preparations include moving their heavy weapons to the hills. Military planners say this is the time to catch them in the open, before they reach the mountain hideouts.
The military operation is expected to be in two phases - an initial attack on bin Laden's al Qaeda network and Taleban forces, to be followed, if necessary, by a wider assault including bombing raids.
President Bush has not ruled out broadening the war on terror to include an attack on Iraq, regarded by Washington as a state sponsor of terrorism, as part of the second stage of the military campaign.
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America
