Pakistani police say a bomb has struck a mini-bus in a northwestern tribal region, killing seven passengers.

Senior officer Shafqat Malik says four people were also wounded in Thursday's bombing on the outskirts of Peshawar, the capital of Khyber-Pakhtunkhwa province.

Malik says the bomb was apparently planted under a bus seat and that police were investigating.

No one immediately claimed responsibility for the attack, which comes as the Pakistani military is waging a major offensive against the Pakistani Taliban and foreign militants in the North Waziristan tribal region near Afghanistan.

The army says militants have been on the run since the June launch of the operation, which also displaced over 800,000 people. Most of the displaced have been living with relatives or at camps in the northwest.