US-led forces have killed at least 21 civilians in an air strike in southern Afghanistan, local officials say.
US forces said they called in air support
Helmand provincial Governor Asadullah Wafa said civilian homes were bombed in Sangin district, where foreign and Afghan troops are battling the Taleban.
The US-led coalition said one of its troops died in fighting in Sangin, but it had no reports of civilian deaths.
Mounting civilian casualties have caused an outcry in Afghanistan, with foreign forces accused of carelessness.
Wednesday's reported deaths came a day after the US military said it was "deeply ashamed" over the killings of 19 Afghan civilians by US Marines in early March.
The apology came as the Afghan Senate called on the government in Kabul to open direct talks with local Taleban militants, and for attacks on them to stop.
Public discontent in Afghanistan is growing over the rising number of civilian casualties and the government's failure to improve the lives of most Afghans.
In January, Nato said its biggest mistake last year had been killing civilians, and promised to do better.
Mr Wafa said said international forces were ambushed by Taleban insurgents on Tuesday afternoon, and air strikes were called in later against three villages.
He said women and children had been among those killed when planes attacked in support of Nato troops trying to drive militants from the lawless, opium-producing region of Sangin.
There have been frequent protests against civilian deaths
Nato said it was "unaware, at this time, of any Nato air strikes resulting in civilian casualties over the past 24 hours".
A statement from the American-led task force in Afghanistan, which works outside Nato command in counter-terrorism operations, confirmed that US special forces were in the area.
It said they had been working alongside the Afghan national army and had come under mortar, rocket and small arms fire while on patrol 25km (15 miles) north of Sangin.
"Coalition close air support aircraft destroyed three enemy command and control compounds including an enemy underground tunnel network located along the upper Sangin River Valley," a statement said.
A US military spokesman Maj William Mitchell told the Associated Press news agency that the troops had killed a "significant" number of militants.
"We don't have any report of civilian casualties. There are enemy casualties - I think the number is significant," Maj Mitchell said.
Residents of the bombed area said Western troops and Afghan forces were preventing people from entering.
Correspondents say that casualties in remote battle sites in Afghanistan are almost impossible to verify.
Taleban fighters are often accused of seeking shelter in peoples' homes, leading to civilian casualties, and it is often difficult to determine if people killed in such air strikes were militants or civilians.
One local resident told the BBC that a number of bodies had been taken to the British base in Sangin to show they were not Taleban fighters.
But British forces would not confirm this.
Nato said their helicopters were helping to airlift injured civilians for hospital treatment.
The fertile Sangin Valley is strategically important
The BBC's Alastair Leithead in Kabul says there have been a number of incidents in the past few weeks where US special forces outside Nato remit have been blamed for killing civilians.
In the worst incident, more than 50 civilians were reported killed in the western province of Herat last week.
President Hamid Karzai recently warned of "dire consequences for all" if civilian killings continued.
As details of the fighting in Sangin emerged, Nato announced it would allow more involvement by the Afghan government in the planning of operations, and that a system would be set up to investigate claims of civilian casualties.