The US military says that Taliban fighters prevented civilians from fleeing clashes in southern Afghanistan, leading to the deaths of about 40 people, believed to have been attending a wedding ceremony, reported Aljazeera.
US and Afghan forces killed several Taliban fighters in the battle, which took place in Kandahar, the US military said on Thursday.
The military did not specify how many civilians were killed in the fighting, but villagers say that about 37 civilians died in a US air raid on Monday.
The bombing run was called in as part of the fighting between US forces and Taliban fighters in the area.
The military's statement said that fighters attacked a US-led patrol that was moving through the Shah Wali Kot region of Kandahar between Monday and Wednesday.
"Civilians reportedly attempted to leave the area, but the insurgents forced them to remain," the US military said, but did not specify where the report was from.
Hamid Karzai, the Afghan president, condemned on Wednesday the killings, saying that 40 people had been killed and 28 wounded as a result of an air raid.
Karzai also called for Barack Obama, the US president-elect, to ensure that Afghan civilians are not killed in operations by US forces.
Roozben Khan, the father of the bride at the wedding ceremony in Shah Wali Kot district, which US fighters allegedly bombed, said that he had lost six relatives in the attack.
"I lost two sons, two grandsons, a nephew, my mother and a cousin," Khan said.
His daughter was among seven of his relatives who were wounded. The groom survived but his father, mother and sister were killed, he said.
US officials also confirmed that a number of civilians had been killed in the attack and said that an investigation was under way.
But the US military statement alleged that Taliban fighters were responsible for any civilian deaths because they had prevented civilians from fleeing.
"Witnesses reported seeing insurgents firing machine guns, rockets and RPGs [rocket propelled grenades] from the rooftops of buildings in the area, as well as mortar teams firing around the ambush site," US forces statement said.
Major John Redfield, a spokesperson for the US forces in Afghanistan, told Al Jazeera from Kabul: "This is an issue we take very seriously, we go to great lengths to prevent any civilian casualties but the Taliban often operate from civilian areas and sometimes draw fire there.
"But we are going to investigate this."
Redfield said that a joint investigation would be made with the Kandahar governors office, the national directorate of security and the regional police office."
Concerning the use of air strikes, he said: "We have to use any means possible against an enemy like the Taliban. We take great measures to ensure that areas are free of civilians."
The international forces in Afghanistan regularly say that Taliban fighters do little to try to protect non-combatants, but this has done little to ease growing anger in Afghanistan over civilian casualties.
The US air raid is the latest in a string of incidents in which the US military has been accused of attacking civilians.
In one of the most serious cases of civilian deaths in Afghanistan, an Afghan government commission found that a US operation in August in western Afghanistan killed some 90 civilians.
The US at first denied that any civilians had been killed, but after two investigations and the emergence of photographic evidence of dozens of bodies - including children - the US said that 33 civilians had died.