WASHINGTON, Dec 10: The Pentagon acknowledged on Friday that even fortified armour cannot protect US troops from improvised explosive devices Iraqi guerillas are using against them.

A senior Pentagon official, Lt Gen Steven Whit comb, told a briefing that the guerillas have devices that are detonated under the vehicles and knock them out.

To overcome this weakness, the general said, the Pentagon will continue to improve the armour of military vehicles in Iraq. He said the military had enough resources and was installing additional armour on military vehicles already in Iraq and Kuwait.

Gen. Whit comb stressed that increasing the armour on vehicles is just one part of the army's strategy to protect troops. He said a high priority is finding and stopping the insurgents from building the explosive devices.

The Pentagon's assurance follows an embarrassing encounter between US Defence Secretary Donald Rumsfeld and his troops in Kuwait earlier this week during which the soldiers asked why their vehicles were not adequately protected.

On Thursday, President George W. Bush said the concerns expressed by the soldiers were genuine and assured them that his administration would provide them with "the best possible equipment."

"If I were a soldier overseas wanting to defend my country, I'd want to ask the secretary of defence the same question. And that is, 'Are we getting the best we can get us?' And they deserve the best," Mr Bush told a briefing at the White House.

Following Mr Rumsfeld's encounter with the troops in Kuwait, US lawmakers, including some from the ruling Republican Party, also have started questioning the administration's policy in Iraq.

They have raised questions about why the military had not started armouring its vehicles sooner than August 2003, when insurgents turned to bombs to attack US forces. Some critics point to the lack of light armoured vehicles as further evidence the Bush administration was unprepared for the kind of insurgency it has faced in Iraq.

The most at risk are the big trucks that ferry supplies, troops and even other vehicles through rough stretches of highway between Kuwait and Iraq. The better-known Humvee serves as a light troop carrier, weapons platform and all-purpose jeep. But the big trucks, like the five-ton M939 medium truck and the tank-hauling Heavy Equipment Transporter, face some of the same threats as the Humvees, including roadside bombs and gun and rocket ambushes.

Some have weapons on board, but very few have armour, and of those that do, the armour offers less protection than is carried by many Humvees. To better protect these trucks, US soldiers often have to scavenge outgoing and damaged vehicles for spare armour plates. Besides spare armour plates, the soldiers also use sandbags to enhance protection.

Of more than 9,100 heavy US military trucks in Iraq, Afghanistan and nearby countries, just over 1,100 have received upgraded protection, according to figures provided by the House Armed Services Committee in Washington. Armour add-on kits are in production for many of the rest of these vehicles.

The US military, however, has informed the Pentagon it needs almost 22,000 armoured Humvees in the war area. It has 15,334; an additional 4,400 await armour add-ons and the rest have not been delivered to the region.

Those Humvees are being built at the rate of 450 a month. The company armouring them, Armour Holdings Inc., has pledged to increase production by 50 to 100 vehicles a month.

Humvees are armoured in two ways: at the factory or in the field. The factory-armoured vehicles are considered the best-protected, and the military says it needs 8,105 in Iraq, Afghanistan and nearby countries.

It has 5,910. About 120 have been destroyed. The rest are protected with add-on kits of armour that can be bolted to a regular un armoured Humvee. Manufacturers are making these kits at a rate of 800 a month. Some 4,300 Humvees remain un armoured.