The troops were raiding compounds suspected of housing bomb makers in the Garmser district of Helmand province on Sunday when militants attacked them with heavy fire, the statement said. Coalition forces responded with small-arms fire, killing several militants, it said.
"During one of the engagements, several militants barricaded themselves in a building on the compound and engaged coalition forces with a high volume of gunfire. Coalition forces used a single grenade which killed the attacking militants," the statement said. "However, the building the militants were fighting from collapsed."
After the clash, troops recovered the bodies of a woman and two children from the collapsed building, along with several militants and their weapons, it said. Another woman was wounded during the battle and taken to a medical facility for treatment. Two suspected militants were detained for questioning, the coalition said.
"We would like to express our heartfelt condolences to the families and loved ones of the deceased," said Maj. Chris Belcher, a coalition spokesman.
"When militants knowingly engage coalition forces with innocent people in the background, it only shows the extremists' complete disregard for innocent lives," Belcher said in a statement.
Civilian casualties have incited resentment and demonstrations against U.S. and NATO forces in the past, though officials blame militants for using civilian homes as cover during clashes. President Hamid Karzai has pleaded with Western forces to do all they can to prevent such deaths.
The raid by coalition forces came two days after a Friday ambush on U.S. forces high in the mountains of eastern Afghanistan.
Six U.S. soldiers were killed when insurgents ambushed their foot patrol. A military spokesman says they were on their way back from a meeting with village elders late Friday afternoon in Nuristan province when they were attacked with rocket propelled grenades and gunfire.
"They were attacked from several enemy positions at the same time," said Lt. Col. David Accetta, a spokesman for NATO's International Security Assistance Force and the U.S. military. "It was a complex ambush."
Eight Americans and 11 Afghans were wounded. For the U.S., the 14 total U.S. casualties is the highest number of wounded and killed from a battle in Afghanistan so far this year.
Fighter aircraft and troops using artillery or mortars at nearby outposts fired on the militants' positions, Accetta said. It wasn't immediately clear how many militants were involved in the ambush, he said.
Mohammad Daoud Nadim, Nuristan deputy police chief, said the ambush happened in the remote province's Waygal district, about 40 miles from the border with Pakistan, which militants are known to use as a sanctuary. Nadim said he had no information on any casualties among the militants.
Nuristan has seen heavy fighting in recent months. Two U.S. soldiers were killed and 13 wounded by a militant ambush in July, while militants disguised in Afghan army uniforms wounded 11 U.S. troops and killed two Afghan soldiers in August.
Friday's attack was the deadliest incident for U.S. troops in Afghanistan since a Chinook crashed in February in Zabul province, killing eight Americans. Officials ruled out enemy fire as the cause of that crash.
Violence in Afghanistan this year has been the deadliest since the Taliban's ouster. More than 5,800 people, mostly militants, have died so far this year in insurgency-related violence, according to an Associated Press count based on figures from Afghan and Western officials.