A roadside bomb killed four policemen and wounded eight others as they were travelling in a restive zone of southwest Pakistan on Friday, a top elected official and police said.

The attack happened in the town of Sui in Baluchistan province. No one claimed responsibility, but suspicion fell on separatist groups who have claimed previous such attacks on security forces in the area.

Abdul Qudoos Bizenjo, the provincial chief minister, condemned the bombing and called it an act of terrorism. He vowed to make all efforts to arrest those who orchestrated the attack.

Bizenjo said the slain and wounded were part of a special local police force known as the Peace Force.

The latest attack came two days after militants attacked a security post in Baluchistan, triggering a firefight that killed 10 soldiers and an assailant. Baluchistan has been the site of a long-running insurgency, with an array of separatist groups staging attacks, mainly on government troops and police.

The separatists in the province have been demanding independence from the central government in Islamabad. Although Pakistan's government says it quelled the insurgency, violence in Baluchistan has persisted.