At least six people were killed and three others injured when two roadside bomb blasts hit a passenger van and motorbike in the restive northwest Friday, officials said.

"The incident occurred in Chinori village of the Orakzai tribal district (around 75 miles northwest of Peshawar), the target was the son of a peace committee chief", said a local administration official.

Khushal Khan, a senior administration official, confirmed the incident.

"The first blast hit the motorbike, killing the son of the anti-Taliban peace militia and injuring his friend, while the second blast hit a passenger van killing five people", Khan told AFP.

Nobody immediately claimed responsibility for the attack but the Pakistani Taliban, and its splinter factions, have previously attacked peace committees -- volunteer militia backed by the government to fight against the insurgents.

Pakistan has been battling Islamist groups in its semi-autonomous tribal belt since 2004, after its army entered the region to search for Al-Qaeda fighters who had fled across the border following the US-led invasion of Afghanistan.

In June the army began a long-awaited offensive against militant hideouts in the North Waziristan tribal area, after a bloody raid on Karachi Airport ended faltering peace talks between the government and the Taliban.

Pakistan's army says it has killed more than 1,000 militants and lost 86 soldiers since the start of the operation.

The number and identity of those killed is difficult to verify as there is little regular media access to the conflict zone.