At least 17 people were killed on Friday when a remote-controlled bomb exploded on a bus carrying government officials in Peshawar, the northwestern city of Pakistan, officials said.

The attack took place on a main road in Peshawar, near the frontier tribal areas of the northwest where Islamist militants have their strongholds.

"We have so far received 17 bodies," said the spokesman for the Lady Reading Hospital. "There were several people on the roof of the bus, which was full, so we expect the death toll to rise." The bus was carrying employees of the civil secretariat, said police officials.

A spokesman for Ansar al Mujahideen, a group allied to but not part of the Pakistani Taliban, claimed responsibility for the blast. Abu Baseer said that the attack was in retaliation for US drone strikes.

Islamist violence has been on the rise in Pakistan in recent months, undermining Prime Minister Nawaz Sharif's efforts to tame the insurgency by launching peace talks with the Pakistani Taliban.

Last week, two suicide bombers blew themselves up outside a 130-year-old Anglican church in Peshawar, killing at least 81 people in the deadliest attack on Christians in the predominantly Muslim country.