A bomb ripped through a bus parked at a terminal in southwestern Pakistan on Saturday, killing seven people and wounding six others, police said.

The explosion occurred in Dera Bugti, a tribal town in insurgency-hit southwestern Baluchistan province, police officer Raja Bashir said. The victims were standing around the bus, which had no passengers on board at the time.

Three people were killed at the scene, while four others died later at a hospital, Bashir said.

No one claimed responsibility for the attack, but Bashir suspected rebel tribesmen were behind it.

Authorities regularly blame armed tribesmen for attacks on security forces, gas pipelines and gas fields in resource-rich Baluchistan.

The violence is seen as part of a campaign to press demands that the central government increase royalties paid to locals for resources, particularly natural gas, extracted from their territories.