Peshawar- At least 11 people, including four children, were killed Thursday when a roadside bomb exploded next to a police van in Dir district of North West Frontier Province, police officials said.

The blast took place when the van transporting prisoners to the local jail arrived in the Khwaga Oba area.

Four policemen and three prisoners were killed in the explosion, local police officer Ghulam Mohammad said.

A passing vehicle carrying school girls was also hit in the incident, leaving four of the children dead.

Officials at the hospital said that most of the 15 injured moved there were policemen and children. They feared that death toll might rise as some of the wounded were in critical condition.

Dir is generally a peaceful district but it borders troubled Swat valley where the security forces are currently engaged in fighting against the pro-Taliban militants. (dpa)