At least 18 people, mostly civilians, were killed when a suicide car bomber targeted a convoy of provincial security forces in eastern Afghanistan, an Interior Ministry official said.

Najib Danish, the ministry’s deputy spokesman, said the target of the bomber was a group of guards providing security for US forces in Khost province, but most of the victims were civilians.

No group immediately claimed responsibility, but Taliban insurgents have increased their attacks against Afghan security forces since announcing their spring offensive last month.

The security forces were attacked near the province’s main bus station, said Mr Danish. “Six other civilians including two small children were wounded in the attack,” he added.

The attack, which took place on a road between a bus station and the provincial football stadium, damaged or destroyed about a dozen shops and several vehicles.

The attack came on the first day of Ramadan, the Muslim holy month.

Mubariz Zadran, a spokesman for the provincial governor in Khost, said the casualty number could rise because some of the wounded were in a critical condition.