The U.S. military in Afghanistan has confirmed there were civilian casualties during fighting with Taleban militants in southern Helmand province earlier this week.
The U.S.-led coalition says the exact number of civilian casualties is not known. A joint U.S.-Afghan investigation is underway.
A statement said coalition troops treated up to 20 villagers wounded during the 16-hour battle in Sangin district on Tuesday.
Earlier in the week, a U.S. military spokesman, Major Chris Belcher, said the U.S.-led coalition had no reports of civilian deaths.
The governor of Helmand province said 21 civilians, including women and children, were killed in Tuesday's air strike in Sangin.
Afghan officials say more than 50 civilians were killed during U.S. military operation in western Herat province earlier this month, sparking days of protests by angry villagers.
Also this week, another U.S. military commander, Colonel John Nicholson, apologized to the Afghan families of civilians who were killed by U.S. Marines in March. The families were given $2,000 in compensation for each death.