Four al Qaeda fighters killed in Afghanistan

BAGRAM, Afghanistan (CNN) -- At least four al Qaeda fighters have been killed this week by coalition Special Forces near the eastern Afghan city of Khowst, according to the U.S. military.

On Monday morning, Special Forces were observing a suspected terrorist site northeast of Khowst when they were fired on by three al Qaeda fighters, said Navy Cmdr. Frank Merriman, U.S. Central Command spokesman.

Soldiers returned fire and killed two al Qaeda fighters, said Maj. Bryan Hilferty, a U.S. military spokesman.

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Merriman said the 101st Airborne Division was sent into the area; several caves were discovered, and caches of mortars, grenades and machine gun ammunition were found.

On Tuesday morning, Special Forces killed two more al Qaeda in the same area, Hilferty said.

Hundreds of U.S. and coalition forces Monday stepped up the search through eastern Afghanistan along the Pakistan border to track down suspected al Qaeda troops, U.S. officials said

The campaign has been under way for several weeks, but officials said the effort, known as Operation Mountain Lion, is in a particularly active phase now.

Sources said that U.S. and coalition troops have seen "fresh trails" of enemy forces in recent days and suspect they have seen some al Qaeda fighters at a distance.

"We continue to do active reconnaissance and patrols," one U.S. military official said. "We are going to search places we have been before as well."

Revisiting sites helps U.S. forces determine whether al Qaeda troops are returning to specific areas, the official noted.

The increased activity by U.S. and coalition forces is mostly confined to the Afghanistan border provinces of Paktia and Paktika.

Officials have said a handful of U.S. troops are across the border in Pakistan and continue to help the Pakistanis with communications and liaison work in tribal areas tracking possible al Qaeda forces.