A joint Afghan-U.S. investigation has found that an air strike last week killed 37 civilians and wounded 35 after Taliban militants used the victims' village as cover for an ambush, the U.S. military said, according to Reuters.
President Hamid Karzai said after the incident that mounting civilian casualties was the biggest source of tension with his main backer, the United States.
He called on U.S. President-elect Barack Obama to make it his priority to stop the killing of innocent bystanders.
A string of mistaken U.S. air strikes this year has killed at least 150 Afghan civilians, undermining public support for the continued presence of more than 60,000 NATO-led and U.S. coalition troops in Afghanistan.
Villagers told investigators a large number of insurgents arrived at the village of Wech Baghtu, in southern Afghanistan, and used homes to fire on a joint patrol of U.S.-coalition and Afghan forces, the U.S. military said in a statement.
The militants prevented people from fleeing, the statement released late Saturday said.
The patrol "was taking accurate fire from the high ground and was separated from its relief unit by an improvised roadblock, and used close air support to suppress enemy fire," it said.
NATO and the U.S. military accuse the Taliban of deliberately launching attacks from within populated areas in order to provoke a response that kills civilians.
"We regret this tragic loss of innocent lives and express our condolences to the families and to the people of Afghanistan," U.S. forces spokesman Colonel Greg Julian said in the statement.
In a separate incident, the governor of the eastern province of Khost said an air strike killed 14 Afghan security guards working for a road construction project.
But the U.S. military said instead that 14 suspected insurgents had opened fire when troops attempted to stop their vehicle. U.S.-led coalition forces shot back and, aided by fire from a helicopter, killed them.
A joint investigation with the Afghan Interior Ministry has been launched into the incident, Julian said.
Some 4,000 people, a third of them civilians, have been killed in fighting this year as the Islamist Taliban steps up its campaign to topple Karzai's government and oust foreign troops.