|Al Jazeera's Kamal Hyder reports that the closing of the Pakistan border has left dozens of lorries vulnerable
Suspected Taliban fighters in southwestern Pakistan have set fire to nearly 30 tankers carrying fuel for Nato troops in Afghanistan in the sixth such strike in just over a week, officials said.
At least 20 armed men launched the attack on the tankers, which were parked at a roadside restaurant near the town of Sibi on Saturday.
"The attackers first fired shots and then fired small rockets at the tankers. Twenty-eight to 29 tankers caught fire," Naeem Sherwani, a government official, said.
He said one of the paramilitary soldiers escorting the convoy was wounded.
Armed groups have stepped up attacks on convoys carrying supplies for Nato forces since a cross-border US helicopter raid on September 30 that killed two Pakistani soldiers in northwestern Pakistan.
Border crossing closed
In retaliation for the raid, Pakistan closed a vital supply route for the international forces in Afghanistan and has kept it sealed since, despite a US apology for the death of the soldiers.
The closing of the Torkham border crossing in the Khyber area has left dozens of lorries stranded, making them vulnerable for attacks by the Taliban, Al Jazeera's Kamal Hyder reported from Peshawar.
Pakistan's foreign ministry said after the US apology that security was being evaluated and a decision on reopening the supply route would be taken "in due course".
Lorry routes through Pakistan bring in around 40 per cent of supplies for Nato forces in Afghanistan, according to the US Transportation Command.
Of the remainder, another 40 per cent comes through Afghanistan's neighbours in the north and 20 per cent by air.
Discussing Saturday's attack in the southwest, Talat Masood, a military analyst and former general in the Pakistan army, told Al Jazeera: "While security is the responsibility of the state and the Pakistan military, the individual security of these tankers has been outsourced to companies inside Pakistan, which have been operating for a long time.
"And when these trucks started clustering as a result of the suspension of the route - I think there were hundreds of thousands of trucks which were stranded along the route - they became a very easy target for the militants. And I think there is some criminal activity as well."
Pakistan's relations with Nato are already strained over the intensifying drone attacks in the border regions.
On Friday night, at least five suspected Taliban fighters were killed in the latest such strike in the North Waziristan tribal region.
Osama bin Javaid, news editor for DawnNews, called the US-Pakistan relationship "very fractured" and told Al Jazeera that the increasing number of drone attacks are "the bone of contention between the two states, which are key allies in the war on terror".
Bin Javaid also said that military analysts in Pakistan feel that the US is trying to find a "trophy piece" before leaving Afghanistan.
Pakistan said that there was "no justification nor understanding" for US drone strikes on its soil, which have killed about 150 people in the past month.
"We believe that they are counter-productive and also a violation of our sovereignty," Abdul Basit, a foreign ministry spokesman, said. "We hope that the US will revisit its policy."