At least 12 people have been killed and 25 injured in what police say is a suicide bomb attack in the Hangu district of north-west Pakistan.
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.
Police said that the bomber detonated explosives near a bus full of passengers.
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.
The Parachinar and Orakzai region is home to a large number of Shia Muslims and the area has suffered from sectarian violence in the past.
The Tall-Parachinar road was closed to all traffic for nearly two years in 2008 and 2009 because of Taliban activity in the area and the frequency of attacks on Shia Muslims in the area, correspondents say.
The road was re-opened about two months ago and traffic currently moves in convoys guarded by paramilitary security forces.
Hangu borders Pakistan's volatile semi-autonomous tribal regions, where a number of militant groups are thought to be operating.
But anti-militant operations by security forces in the area has improved security, correspondents say.