A US airstrike in Afghanistan on Tuesday killed as many as 23 civilians, with most victims women and children, the UN says.
The strike on a compound in Helmand province was called in during a joint operation between Afghan and US forces.
Investigators said up to 10 children and eight women may have been killed. US forces say they are investigating.
Civilian casualties from aerial attacks have surged since the US announced a new Afghan strategy last year.
President Trump committed more troops to America's longest war and significantly boosted the number of strikes targeting Taliban and Islamic State group positions in August 2017. The rules of engagement were also loosened, allowing more bombings.
The US-led Nato mission in Afghanistan said that Tuesday's helicopter strike took place amid a firefight between US-advised Afghan special forces and Taliban fighters in Garmser district.
Nato said the Taliban had been using the building that was hit "as a fighting position", and accused the militants of continuously using civilians as human shields.
A local resident who did not want to be named for fear of retaliation told the BBC that Taliban fighters were indeed near the building that was hit by the US strike.
He said the youngest victim was about six years old, but this could not be verified.
The UN Assistance Mission in Afghanistan recorded 649 civilians casualties (dead and injured) as a result of aerial attacks in the first nine months of this year, the highest number in any year since systematic recording began in 2009.
In April, an attack by the Afghan Air Force - which is trained and equipped by the US - killed 30 children in north-eastern Kunduz province at a graduation ceremony.
The US Air Force released nearly 6,000 weapons in the first 10 months of this year, compared to 4,361 in all of 2017 and 1,337 in all of 2016.
Most civilian casualties in Afghanistan are however still caused by anti-government groups like the Taliban and the Islamic State group (IS).
The Taliban are gaining ground across Afghanistan, as US officials pursue a peace deal that would bring an end to the 17-year war.
The militants attended a landmark international meeting earlier this month in Moscow and a delegation from the group has also recently held meetings with US envoys in Qatar.