A US drone strike in Kabul last month killed as many as 10 civilians, including seven children, a senior US general has said.

"It was a mistake and I offer my sincere apology," US General Frank McKenzie, the head of US Central Command, told reporters on Friday.

He added that he now believed that it unlikely that the vehicle hit or those who died were Daesh militants posing a direct threat to US forces at Kabul's airport.

McKenzie said the vehicle was struck "in the earnest belief" that the targeted vehicle posed an imminent threat.

"I am now convinced that as many as 10 civilians, including up to seven children, were tragically killed in that strike," McKenzie said.

US Defense Secretary Lloyd Austin also issued an apology.

"I offer my deepest condolences to surviving family members of those who were killed," Austin said in a statement.

"We apologise, and we will endeavour to learn from this horrible mistake," he said.

READ MORE:'My kids split in half': Afghans seek answer after US strike kill civilians