British forces began sweeping through rugged terrain in southeastern Afghanistan on foot Friday as part of a large-scale operation to hunt down remaining pockets of Al Qaeda and Taliban fighters, a Royal Marines spokesman said. 

The first four days of Operation Snipe had been devoted to gathering intelligence and getting forces from Bagram air base, where thousands of British and American soldiers are based, into position in the southeast, Lt. Col. Paul Harradine said. 

"It's only just starting, at first light this morning, they started the sweep," Harradine told reporters Friday. "They'll be moving through the area looking for caves, looking for bunkers, looking for Al Qaeda and Taliban." 

About 1,000 troops have been deployed in the British-led mission, which is backed by U.S. air support and some U.S. special operations forces. About half the troops are Royal Marines from the 45 Commando unit, the rest are Afghan infantry loyal to the interim administration of Hamid Karzai, Harradine said. 

Coalition forces have been stepping up operations in eastern Afghanistan, along the Pakistani border, but British officers said this was a separate mission in a region that had never been searched by allied forces. Harradine declined to give details about its location, but said it was in a mountainous region. 

Harradine said Royal Marines had found a number of "caves and historic defense positions on the way into their start positions." 

He said no hostility had been shown to the troops by local villagers, some of whom had offered food to coalition soldiers. 

Meanwhile, U.S. military spokesman Maj. Bryan Hilferty said three mortars or rockets exploded at midday Thursday several hundred yards from the airfield at Khost, an eastern Afghan town where a team of U.S. special operations troops has a base. No injuries were reported and it was unclear who fired the rounds, Hilferty said.