ISLAMABAD -- The Pakistani Taliban claimed responsibility Monday for a pre-dawn attack on tankers carrying fuel to Afghanistan for U.S. and other NATO forces, vowing to continue raiding supply lines in Pakistan until they are shut down completely.
The attack came on a supply line that has been stalled because of a temporary border closing imposed by Pakistani authorities after a NATO helicopter attack killed three Pakistan troops last week.
It was the third such attack since Friday, and seemed certain to raise the stakes in the closure, which has exacerbated tensions between Washington and Islamabad but has been welcomed by Islamist groups opposed to Pakistan's support of the U.S.-led war in Afghanistan.
About a dozen militants attacked the tankers as they were parked at a truck stop outside Islamabad, peppering the vehicles with their automatic weapons and then setting the leaking fuel ablaze. Four people were killed and another seven injured, and some 20 trucks were partially or totally destroyed, authorities said.
The Pakistani Taliban, which last week threatened more attacks on the supply lines, claimed responsibility in a telephone call to an Associated Press reporter.
Spokesman Azam Tariq said a new wing of the group had been created to strike the convoys and that the attacks "would continue until the supplies are completely stopped."
Trucks moving supplies from the port city of Karachi through Pakistan into Afghanistan make frequent stops along the way for their drivers to rest along the several-day journey, and Islamabad police chief Kalim Imam said it was impossible for police or local authorities to protect them all the time.
"This entire thing is very vulnerable for such attacks," he said.
The trucks were en route or waiting to travel to the Torkham border crossing along the fabled Khyber Pass, which is used to bring fuel, military vehicles, spare parts, clothing and other non-lethal supplies for foreign troops in Afghanistan. Pakistan's other main route into landlocked Afghanistan, in Chaman in the southwest, has remained open.
While NATO and the United States have alternative supply routes into Afghanistan, the Pakistani ones are the cheapest and most convenient. Most of the coalition's non-lethal supplies are transported over Pakistani soil after being unloaded at docks in Karachi, a port city in the south.
On Friday, a day after the closure of the Khyber Pass route to NATO and U.S. traffic, there were two attacks on oil tankers headed to the country, one of which was claimed by the Pakistani Taliban.
The Pakistani Taliban are the country's largest militant group. Based in the northwest, it has claimed responsibility for scores of suicide bombings against Pakistani government and security targets, as well as Western ones. The group has ties with the Taliban movement in Afghanistan that is fighting the U.S.-backed government there.
Striking the supply line now gains the group more media attention than normal and makes the mission in Afghanistan appear vulnerable.
While attacks on convoys in Pakistan give militants a propaganda victory, coalition officials say they do not result in shortages in Afghanistan. Hundreds of trucks cross into Afghanistan each day.
Some attacks are believed to be the work of criminals, who can sell much of the vehicles, clothes and other goods they carry. Officials have alleged truck owners may be behind some of the incidents, perhaps to claim insurance fraudulently.
On Sunday, Pakistan's ambassador to the U.S., Husain Haqqani, said the border crossing would be soon reopened.