Between 40 and 50 suspected Taliban militants have been killed in heavy fighting with Afghan forces backed by U.S. attack helicopters and "tank buster" aircraft near the Pakistan border, the U.S. military said on Tuesday.

The casualty figure, based on estimates by pilots flying in support of Afghan soldiers in the fighting on Monday, came in a statement from the U.S.-led force of 18,000 troops hunting al Qaeda and Taliban guerrillas in Afghanistan. It gave no concrete details for the figure.

If confirmed, it would be one of the heaviest losses in recent months from a single battle for the insurgents fighting foreign and Afghan forces in Afghanistan.

A local commander in Khost, near the site of the clashes that erupted in the early hours of Monday, told Reuters on Monday he knew of two Afghan soldiers and two Taliban guerrillas killed. The U.S. military said 50 insurgents attacked Afghan soldiers using rockets, mortars, rocket-propelled grenades and machine guns.

In a second assault some five hours later, between 20 and 50 militants struck in the same area.

"The exact number of enemy casualties is unknown, but pilots flying overhead estimated that approximately 40-50 insurgents were killed," it said.

Local commander General Khialbaz Sherzai said on Monday his forces saw suspected Taliban militants retreat over the border into Pakistan, many apparently wounded.

Pakistan denies Afghan accusations that its territory is being used as a sanctuary by militants.

Remnants of the Taliban, ousted in a U.S.-led war in 2001, have declared a "jihad," or holy war against foreign forces, Afghan troops, government officials and aid workers.

The Taliban have vowed to disrupt preparations for elections in October and April.

U.S.-led forces sent a B-1 bomber, A-10 Thunderbolt II "tank buster" aircraft and attack helicopters to support Afghan soldiers in the latest clashes.

Source: Agencies