Special forces have begun a secret mission to capture or kill Osama bin Laden, the prime suspect in the US terror strikes.

Senior US and Pakistani officials said the Special Operations Forces had begun moving into countries bordering Afghanistan, where the terrorist was in hiding.

Teams of soldiers were expected to start entering Afghanistan's mountainous regions within days to try to locate bin Laden, who is believed to be hiding in caves or underground bunkers.

The teams of three to five camouflaged soldiers were believed to involve American troops, although military experts have said Britain's elite SAS forces would be involved in the planning or execution of any special forces mission.

A special operations command centre has been set up in the region to coordinate the mission, the officials said.

They said bin Laden was believed to be in south west Afghanistan, but said it was not clear where.

The claims of special forces troops moving into Afghanistan came amid reports that America had sent two Hercules transport planes to Uzbekistan.

The giant planes are capable of transporting vast amounts of supplies and support systems, and play a vital part in any military build-up.

President George Bush said in his speech to Congress early yesterday that the "hour is coming when America will act", and told US military forces: "Be ready."

And his government is pressing European allies to agree to a military campaign to overthrow Afghanistan's ruling Taliban regime and replace it with an interim administration.

It is understood that diplomatic cables from a key Nato ally said the US wanted to hear views on "post-Taliban Afghanistan after the liberation of the country".

The cable, from the Washington DC embassy of a Nato country, showed that the US wanted to topple the Taliban from power because it had harboured bin Laden.

The US Government was funding figures within the Afghan opposition group the Northern Alliance, and could encourage its guerilla army to support the country's exiled monarch, King Zahir Shah.

"The king plans to call on all the Afghan tribes to rise up against the Taliban," the diplomatic cable reportedly said. Prime Minister Tony Blair suggested that military strikes inside Afghanistan, targeted on bin Laden's training camps, could come in a matter of days.

But air strikes in the region could prove difficult as Turkmenistan which granted permission for the Hercules planes to fly over it did not want to give similar rights to fighter aircraft, and they could not fly over Iran.

Military preparations to date have included the deployment of more than 100 warplanes to the Gulf, including F-16 and F-15 ground attack aircraft, and mobilisation orders for commando forces.