Pakistani Taliban on Monday claimed responsibility for two attacks on NATO supply convoys in Pakistan and threatened to carry out more.
"We accept responsibility for the attacks on the NATO supply trucks and tankers," Tehreek-e-Taliban Pakistan (TTP) spokesman Azam Tariq told AFP.
"I am talking about attacks both in Sindh and in Islamabad," he said in a telephone call from an undisclosed location.
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"We will carry out more such attacks in future. We will not allow the use of Pakistani soil as a supply route for NATO troops based in Afghanistan.
"This is also to avenge drone attacks," he added.
Three killed, twenty tankers destroyed
At least three people were killed when about 20 oil tankers loaded with fuel for NATO troops in Afghanistan were attacked and set ablaze near the Pakistani capital overnight, police said.
The attack came as Pakistani authorities continued their own blockade of a main land route for NATO supplies for a fifth consecutive day, allegedly in response to a NATO helicopter strike that Islamabad says killed three of its soldiers.
On Monday, NATO chief Anders Fogh Rasmussen urged Pakistan to reopen the key Afghanistan supply route as soon as possible, and expressed regret for the deaths of the Pakistani troops.
He says NATO and Pakistan needed to improve cooperation on the Afghan-Pakistani border region to prevent Taliban insurgents from crossing the frontier to attack foreign troops fighting in Afghanistan.
Flamers leap from trucks
Television pictures had earlier shown flames towering from the trucks. The trucks were being filled just outside Islamabad en route to Afghanistan early in the morning when gunmen attacked the convoy with molotov cocktails.
In a similar incident on Friday in the south, heavily armed gunmen set ablaze more than two dozen trucks and tankers carrying fuel for the 152,000-strong foreign force fighting the Taliban-led insurgency.
"Three people have died, eight are injured. They have all received bullet injuries and are mostly drivers and their helpers," police emergency official Mohammad Ahad told AFP by phone after the latest incident.
Attackers flee scene
Police said around a dozen people who attacked the supply tankers fled the scene.
Ambushes of NATO convoys are not uncommon, but are normally concentrated in strongholds of Islamist militants in the lawless northwest.
An administrative official at Torkham, the main border crossing, confirmed the blockade was continuing for a fifth day.
Queues of more than 200 trucks and oil tankers have formed at the northwestern Khyber pass border as they wait to deliver supplies.
Washington has described Pakistan's tribal belt on the Afghan border as a global headquarters of Al-Qaeda, a hub of militants fighting in Afghanistan and the most dangerous place on Earth.
More than 3,700 people have been killed in the last three years in a series of suicide attacks and bomb explosions in Pakistan, many of them carried out by the Taliban and other Al-Qaeda-linked Islamist extremists.
