Daybreak brought the sporadic crackle of gunfire. Medical helicopters circled overhead and landed, indicating possible early casualties among the Marines.

A marine unit in Nawa traded gunfire with a group of some 20 insurgents, while Afghan troops exchanged small arms fire with militants after they were attacked with rocket propelled grenades fired from several houses. A Cobra helicopter circling overhead for most of the day fired rockets at a tree-line nearby. Other troops walked through fields of corn and past mud-wall homes. Only a handful of villagers dared to venture outside.

A roadside bomb early in the mission wounded one Marine, but he was able to continue, spokesman Capt. Bill Pelletier said.

Southern Afghanistan is a Taliban stronghold but also a region where Afghan President Hamid Karzai is seeking votes from fellow Pashtun tribesmen.

The Pentagon is deploying 21,000 additional troops to Afghanistan in time for the elections and expects the total number of U.S. forces there to reach 68,000 by year's end. That is double the number of troops in Afghanistan in 2008, but still half as many as are now in Iraq.

The Taliban, who took control of Afghanistan in 1996 and were ousted from power following a U.S.-led invasion in 2001, have made a violent comeback, wreaking havoc in much of the country's south and east, forcing the United States to pour in the new troops.

Pelletier said troops in Thursday's operation were sent in by a mixture of aircraft and ground transport under the cover of darkness.