At least 27 tankers carrying fuel for Nato troops in Afghanistan were attacked in southern Pakistan.
The attack took place on the edge of Shikarpur town in Sindh province yesterday, the same day Pakistan closed a major border crossing to protest over a Nato incursion into its territory that killed three Pakistani soldiers.
No-one is believed to have been killed or wounded in the tanker attack.
Police official Mir Ahmed Chandio said the tankers were parked at a terminal when gunmen opened fire, forcing people to flee before setting the vehicles on fire.
An Associated Press photographer at the scene said the trucks were still alight several hours after the attack.
Nisar Ahmed, a police official from Shukarpur, said the tankers had arrived in Shikarpur from the southern port city of Karachi and were heading to Quetta, a major city in the south west. From there, they probably would have used the Chaman border crossing.
Chaman remains open, unlike the Torkham border crossing, which Pakistan ordered closed to Nato trucks yesterday.
Chaman has seen fewer attacks than Torkham, but the shutting of one point of entry to Afghanistan creates a bottleneck militants can easily exploit.
Militants and ordinary criminals frequently attack Nato supply trucks as they travel across Pakistan to landlocked Afghanistan. US and Nato move the vast majority of their non-lethal supplies through Pakistan, but have long insisted the attacks have had relatively little impact.
Recent alleged Nato helicopter intrusions on Pakistani soil have raised tensions, however. Yesterday Pakistan said two Nato choppers fired on one of its border posts in the north west’s Kurram tribal region, killing three Pakistani soldiers.
It closed the Torkham border crossing, which connects Afghanistan to Pakistan’s Khyber tribal region, soon after news of the attack emerged.
Nato said its helicopters entered Pakistani airspace and hit a target only after receiving ground fire. The alliance expressed condolences to the families of the soldiers and said both nations would investigate the incident.