A US airstrike in Afghanistan against Taliban militants earlier this week killed 23 civilians and the majority of victims were women and children, the UN said in its preliminary findings on Friday.
The strike on a compound in Helmand province was called in during a joint operation between Afghan and US forces on Tuesday, TOLO News reported.
The UN Assistance Mission in Afghanistan (UNAMA) in a statement said up to 10 children and eight women might have been killed in the strike.
Three children were reportedly injured. US forces said they were investigating the incident.
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.
The UNAMA recorded 649 civilian 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 -- trained and equipped by the US -- killed 30 children in Kunduz province at a graduation ceremony.
The US Air Force released nearly 6,000 weapons in the first 10 months of 2018, compared to 4,361 in all of 2017 and 1,337 in all of 2016.
Most civilian casualties in Afghanistan were, however, still caused by anti-government groups like the Taliban and the Islamic State group, the report said.
The UN statement reminded "all parties to the conflict to uphold their obligations to protect civilians from harm".
It said that all parties to the conflict must strictly adhere to their obligations under international humanitarian law to take all feasible measures to protect civilians.