A US air strike killed 16 Afghan police and wounded two others in Helmand province, officials said on Saturday.
The incident took place on Friday as Afghan security forces were clearing a village of Taliban elements, said Helmand police spokesman Salam Afghan.
"In the strike, 16 Afghan policemen were killed including two commanders. Two other policemen were wounded," he said.
It occurred in Gereshk district in Helmand, large parts of which are under Taliban control.
U.S. confirms Afghan casualties resulting from airstrike pic.twitter.com/DPlPd95nPb— USForces Afghanistan (@USFOR_A) July 21, 2017
NATO's mission in Afghanistan issued a statement.
"During a US-supported (Afghan security) operation, aerial fire resulted in the deaths of the friendly Afghan forces who were gathered in a compound," it said.
"We would like to express our deepest condolences to the families affected by this unfortunate incident," the statement said, adding there would be a probe into what happened.
How many "errant" US strikes so far in Afghanistan?— Mosharraf Zaidi (@mosharrafzaidi) July 22, 2017
Counting may be inconvenient.
Maybe easier to just blame Pakistan for everything. https://t.co/aebpYMAlAJ
52 air strikes in five days
The US is the only foreign force in the coalition conducting air strikes in Afghanistan.
It has carried out 52 air strikes in Helmand over the past five days, including 10 in Gereshk on Thursday, according to US military headquarters in the Afghan capital Kabul.
Earlier this week, Afghan security forces backed by US air strikes retook Nawa district south of Lashkar Gah.
On Thursday, Taliban insurgents attacked security perimeters set up around Gereshk, blowing up three captured Humvees packed with explosives.
MSF reopens medical clinic
Medicines Sans Frontiers (MSF) reopened a small medical clinic in Kunduz on Saturday, their first facility there since US air strikes that destroyed a hospital in 2015.
"The opening of this clinic is the first step toward providing more medical assistance in Kunduz," Silvia Dallatomasina, head of programmes for MSF in Afghanistan, said. "And for us, it's an important step."
Since the attack by US special forces in 2015 which killed 42 patients, medical staff and caregivers at the MSF trauma centre, the medical aid group has been trying to secure assurances from the US and Afghan militaries and security forces that their medical facilities will be respected and protected.
"We are still finalising commitments, but we believe we were able to reach an agreement," Dallatomasina said.