|There has been a string of attacks in Pakistan on lorries carrying supplies for Nato troops [Al Jazeera]
The Pakistani Taliban have claimed responsibility for an attack on fuel tankers carrying supplies for Nato troops in Afghanistan.
The claim came amid a string of attacks targeting supplies for foreign forces passing through Pakistan in recent days.
The Taliban said its fighters had carried out the pre-dawn assault on fuel tankers at a depot near Islamabad early on Monday, killing three guards and setting ablaze 20 tankers. The group also vowed more such attacks.
"We will continue such attacks all over the country to avenge drone attacks and attacks by foreign forces inside Pakistani territory," Azam Tariq, a Taliban spokesman, said.
In another attack during the day, armed men on motorbikes opened fire on a Nato convoy, burned two lorries and killed a driver.
Supplies transported through Pakistan are crucial for foreign forces based in Afghanistan.
About half of all non-lethal supplies for Western forces in land-locked Afghanistan pass through Pakistan, giving Pakistan considerable leverage over the United States, which is scrambling to contain a raging Taliban insurgency in Afghanistan before it starts withdrawing troops in July next year.
Kamal Hyder, Al Jazeera's reporter in Islamabad, said: "Trucks parked in a particular area are soft targets, anybody can go and attack these trucks".
Pakistan said the border has been closed for security reasons and the Taliban threat of more attacks will likely prolong the closure of the vital supply route - now in its fifth day - and further strain ties with Washington, which has long demanded Pakistan crack down on fighters.
The border closure has the approval of a large section of Pakistanis, who have been angered by repeated Nato air strikes on Pakistan's soil. One such Nato raid last week killed three Pakistani soldiers.
On Monday, another Nato strike killed eight anti-government fighters in the Mir ali area of North Waziristan. According to the Reuters news agency, five of those killed were Germans.
Nato on Monday offered an apology for the Pakistani soldiers' deaths to assuage growing resentment.
"I expressed my regret for the incident last week in which Pakistani soldiers lost their lives," Anders Fogh Rasmussen, the Nato secretary-general said after meeting Shah Mehmood Qureshi, the Pakistani foreign minister, in Brussels.
But Al Jazeera's Hyder said the pressure on the Pakistani government to keep the supply route close is likely to be tremendous.
"There has been talk recently that people should go sit on the highways in a peaceful manner and say they will not allow these supplies to pass through Pakistan until Nato and the Americans start to respect Pakistan's sovereignty.
"So the government is under great pressure from that public opinion, that's why for the first time, they have actually closed the Torkham border."
Supply convoys destined for Nato barracks have to travel 10 to 12 days through Pakistan before they can enter Afghanistan through the Torkham border.
Stretching about 1800km, the supply line is long and remains vulnerable to attacks by Taliban and other allied groups.