The attack targeted a convoy of 140 vehicles travelling from Tall in the Hangu district to the town of Parachinar in the Kurram region.

No-one has yet said they carried out the attack.

Pakistan's North West Frontier Province has witnessed numerous bombings by insurgents over the past year.

A suicide attack on a police station in the Karak area of north-west Pakistan killed three people last week.

The convoy was carrying groups of people as well as vehicles loaded with general provisions and other trade goods. Most of the passengers in the convoy were Shia Muslims.