KABUL, Afghanistan (CNN) -- Troops with the NATO-led force in Afghanistan killed three bus passengers Friday after the vehicle veered toward their patrol, the force said in a statement.
The patrol fired warning shots after the bus turned toward them along the highway from Kandahar to Kabul, the International Security Assistance Force said.
Troops fired at the bus when it failed to stop despite the warning shots, including first firing at the vehicle's engine block, the NATO-led force said.
The incident happened in the Abad District of Wardak province southwest of Kabul.
The NATO force said an investigation is under way.
In two operations in southern Afghanistan, Afghan security forces and coalition troops killed five militants and destroyed roadside bombs and bomb-making material.
A policeman was killed and another was wounded in the operations, which took place Thursday and Friday in Helmand province's Nahr Surkh district.