NATO said Saturday a US air strike "may have" hit a hospital run by the medical charity Doctors Without Borders (MSF) in the embattled Afghan city of Kunduz.

"US forces conducted an air strike in Kunduz city at 2:15 am (local time)... against individuals threatening the force. The strike may have resulted in collateral damage to a nearby medical facility. This incident is under investigation," a NATO statement said.