Gunmen in eastern Afghanistan attacked passing vehicles on a darkened highway during a midnight assault Tuesday, killing at least 13 people, authorities said.

The attack happened in Wardak province's Sayad Abad district, where Taliban fighters hold much territory and launch frequent attacks on security forces. However, no group immediately claimed responsibility for the assault, which comes after several recent attacks targeting buses in the country.

The gunmen opened fire on three separate vehicles in the attack, including a bus traveling from Kabul and heading to Ghazni province, said Attahullah Khogyani, a spokesman for the provincial governor. He gave the death toll and said the gunfire wounded at least two civilians.

Last month, gunmen in southern Afghanistan kidnapped 30 members of the Hazara ethnic community traveling on a highway in Zabul province. Security forces have been trying to secure their release ever since the attack, the latest to target Shiites in the predominantly Sunni country

Afghan forces have taken the lead in securing the country after U.S. and NATO troops formally ended their combat missions in the country at the start of this year.