We knew how they would react once the sun went down... so we were ready for that and we killed two

Major General Franklin L Hagenbeck

The BBC's Ben Brown, at Bagram airbase near Kabul, says the latest clashes come amid fears that al-Qaeda may try to use the improving weather in Afghanistan to launch a spring offensive.

General Hagenbeck said the clashes happened on Monday and early Tuesday near the eastern Afghan city of Khost.

The suspected al-Qaeda members had grouped together in a complex of buildings and caves about two kilometres from the Pakistani border which was under surveillance by special forces.

The reconnaissance team came under fire and in the ensuing gun battle killed or wounded two of their attackers, the general said.

The US army then saturated the area with troops, airlifting in 200 soldiers from the 101st Airborne Division.

Fighters escaped

But by the time they got there, the fighters had all fled, possibly across the border into Pakistan, where they often seek sanctuary. The two casualties had also been dragged away.

However, General Hagenbeck said two more fighters were killed early on Tuesday when they ran into an ambush set for the larger group.

"We knew how they would react once the sun went down last night. So we were ready for that and we killed two... as they were coming back through the area," he said.

As General Hagenbeck was speaking at Bagram air base, officials in Canberra said that soldiers of the Australian Special Air Service Regiment had shot two al-Qaeda fighters in Afghanistan.

It was not immediately clear whether the two announcements concerned the same events.

A US army spokesman said they found large quantities of arms and ammunition in the complex, including mortars, grenades and machine gun ammunition.

Border targeted

The location of the fighting has added weight to reports that many Taleban and al-Qaeda fighters have moved to areas near the Pakistani border.

US-led forces now appear to be concentrating their search in the border area where caves often start in Afghanistan and end in Pakistan.

The latest clashes happened in the same region where the last major battles against the Taleban and al-Qaeda were fought in March during Operation Anaconda.

There are now thousands of American, British and other coalition troops in Afghanistan.