In the southern province of Helmand, local authorities said at least 14 civilians, including women and children, were killed and six injured in an air raid on Saturday. US Marines in Helmand's Nawzad district called in air support after their base came under attack from small arms fire, the provincial government said in a statement.
"During the air strike, two civilian houses were targeted which killed 14 civilians and six others were wounded," it said.
The statement said the dead included five girls, seven boys and two women.
"ISAF are aware of the reports that civilians were allegedly killed in an ISAF air strike," Major Tim James, a spokesman for the Nato-led International Security Assistance Force, told AFP.
"(The) Regional Command South West has sent a joint assessment team to the area to look into the allegation and they will issue their findings to the press."
Aslam, a local elder of Nawzad district, told AFP he "lost 12 relatives while 10 others including children were injured" in the air strike. He said some shots were fired at ISAF helicopters which flew into the area, adding that the choppers returned after 10 to 20 minutes and fired rockets, killing the "innocent civilians". According to him, five children, five men and two women were killed in the attack.
Separately the governor of Nuristan on Sunday told AFP that 18 civilians and 20 police were killed by "friendly fire" during US-led air strikes against insurgents in his troubled north-eastern province.
Nuristan was the scene of heavy battles last week between the Taliban and Afghan security forces. The police and civilians were targeted Wednesday after they were mistaken for militants, Jamaluddin Badr said.
"The policemen were killed due to friendly fire," Badr said, adding the air strike in the troubled district of Do Ab targeted a location that the officers "had just" taken from the insurgents during fighting.
"Civilians were killed because the Taliban... (who) ran out of ammunition fled into the civilians' houses and then the civilians were mistaken with the Taliban and fired upon," the governor said.
Major James said those allegations were also being investigated.
"ISAF has sent a fact-finding team to investigate the allegations about civilian and police casualties in Nuristan," he said. "Our initial reporting does not indicate civilian casualties in that air strike," he added.
Meanwhile, Afghan President Hamid Karzai called on the US military to avoid operations that kill civilians, saying it was his "last warning" to Washington after 14 people allegedly died in an air strike.