SURMAD, Afghanistan -- U.S. warplanes hit al-Qaida and Taliban mountain strongholds in eastern Afghanistan on Monday while hundreds of coalition ground troops scoured the rugged, snow-covered terrain for pockets of enemy fighters.
The heavily armed defenders responded with bursts of mortars, grenades and machine gun fire.
Seven Americans died Monday when two helicopters took enemy fire in the offensive -- code-named Operation Anaconda. The attack marked the first time U.S. conventional ground troops have been used in an offensive operation.
The offensive, which includes about 2,000 Afghans, Americans and special operations forces from six allied nations, is the largest U.S.-led ground operation of the five-month Afghan war.
Wave after wave of B-52s and other aircraft unleashed bombs for a fourth day to try to weaken enemy positions in the snowcapped peaks.
"In one minute, I counted 15 bombs," Rehmahe Shah, a security guard at the intelligence unit in the provincial capital Gardez, said Monday.
In Tampa, Fla., Gen. Tommy Franks, commander of U.S. forces in Afghanistan, said units of the 10th Mountain Division and the 101st Airborne Division had been inserted into the battle area.
Franks wouldn't say how many al-Qaida and Taliban were holed up in the labyrinth of caves and ravines at the base of the mountains.
The commander described the ground operation as a series of short, intense clashes fought in bitter cold at elevations of 8,000 to 12,000 feet.
Neither the former Taliban supreme leader Mullah Mohammed Omar nor al-Qaida chief Osama bin Laden was believed to be in the area.
About 40 U.S. troops, including 11 injured Monday, have been wounded since the operation began Friday night in the snow-covered mountains southwest of Gardez.