There was no immediate claim of responsibility, but the Taliban have vowed to step up attacks on security forces in the region to avenge a fresh offensive in the tribal district of Mohmand.

"A roadside improvised explosive device exploded as an army vehicle passed by in Janikhel town, killing two soldiers and wounding four others," a senior military official told AFP.

An intelligence official in the area confirmed the incident and casualties, about 150 kilometres (95 miles) south of Peshawar, the capital of the northwest.

Just north of Peshawar, another roadside blast struck a police van, killing one policeman in the Mithra area.

Police official Muhammad Ejaz said three other policemen were also injured.