A bomb striking a Pakistan Air Force bus in Peshawar killed at least 13 people, mostly security personnel, and injured around two dozen on Tuesday, officials said.

The bomb exploded when the vehicle was passing over a bridge on the outskirts of the city.

"It was a remote-controlled explosive device which was planted under the bridge," said Inspector General of Police Malik Naveed.

TV footage showed pools of blood on the scene, with rescue service personnel trying to put out the fire that gutted several vehicles.

Khizar Hayat, a medical officer at the Lady Reading Hospital, said 11 bodies were brought to the hospital while two of the victims succumbed to their injuries there.

Another 11 injured were being treated at the hospital, four of whom were said to be in critical condition.

Most of the dead were security personnel from the Pakistan Air Force (PAF), said another medical officer Ghareeb Ullah.

No one has claimed responsibility for the attack but the authorities believe it could be carried out by the militants in Pakistan's tribal region bordering Afghanistan.

"Apparently, it seems linked with the situation in tribal areas," said Naveed.

Fighter jets from PAF and gunship helicopters pounded several militants' positions in Bajaur tribal district on Monday, killing at least 50 rebels and taking the death toll in five days of fighting to more than 160.

Taliban rebels had vowed to take revenge for the military action in the district, where clashes erupted last week when hundreds of militants surrounded a paramilitary base in Loi Sam area.