Bin Laden is believed to be hiding in caves

Mr Rumsfeld also said the US was seeking to base heavily-armed AC-130 gunships in Uzbekistan on Afghanistan's northern border, while the US navy has been ordered to search ships off the Pakistani coast if they are suspected of carrying Bin Laden.

The slow, low-flying AC-130 aircraft, which fire a deadly 2,500 rounds of ammunition per minute, has already been used in the war in Afghanistan to attack Taleban troop concentrations and convoys of vehicles.

"It would be helpful to have AC-130s up north, particularly when you have a situation like Kunduz," said Mr Rumsfeld.

Thousands of Taleban fighters, holed up in the northern city of Kunduz, have been bombarded by US aircraft and Northern Alliance artillery.

Hunt stepped up

The defence secretary recently announced plans to beef up the number of US special forces hunting for Bin Laden on the ground in Afghanistan.

AC-130: Used to deadly effect

The main suspect behind the 11 September suicide attacks on New York and Washington has proved elusive and is believed to be hiding in a network of specially-built caves.

Mr Rumsfeld said the Global Hawk was still in the development stages and had never been used in a real operation before.

Built by US-defence firm Northrop Grumman, the Global Hawk flies at 350 miles an hour and can cruise at up to 65,000 feet.

The US has already used another reconnaissance drone in Afghanistan - the $3.2m Air Force RQ-1B Predator - but the Global Hawk is faster and has more than twice the Predator's range.

America's air force has a fleet of four Global Hawks, with two more in production, ready for use next year.