Afghan authorities said Sunday Nato had killed 52 people, mostly civilians, in air strikes against insurgents as violence picked up in recent weeks with the start of the fighting season.
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 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 northeastern 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.
Civilian casualties in the US-led war against Al-Qaeda-linked Taliban insurgents are a sensitive issue and one of the main causes of a widening drift between President Hamid Karzai and his US backers.
Karzai on Saturday ordered Defence Minister Abdul Rahim Wardak to take over control of night raids from the Nato forces.
Karzai's administration says most civilian casualties occur during such operations and that night raids of civilian homes drive war-weary Afghans against his already-fragile administration.
The latest allegations came after general Mohammed Daoud Daoud, the chief of police for northern Afghanistan and a key figure in recent Afghan history, and two German soldiers were among six people killed Saturday by a suicide bomber.
The commander of Nato forces for northern Afghanistan, German general Markus Kneip, was slightly injured but survived the attack at the office of the Takhar provincial governor, German defence minister Thomas de Maiziere said.
The Taliban claimed responsibility in what was their latest example of high-profile target selection.
There are around 130,000 Nato-led foreign troops in Afghanistan, fighting a Taliban-led insurgency launched after the 2001 invasion brought down their Islamist regime in Kabul.