ISLAMABAD, Pakistan -- Armed men torched dozens of NATO fuel tankers in southern Pakistan on Friday, police said, as supply convoys remained blocked at a vital entry point to Afghanistan for a second consecutive day.

Police in the town of Shikarpur said 10 "extremists" shot and set fire to at least 30 NATO trucks stopped at a filling station, destroying the vehicles but injuring no one. Much of the fuel and other supplies bound for coalition forces in Afghanistan arrive at the southern port of Karachi, then are trucked north toward border points at Torkham or Chaman.

In the southeastern province of Baluchistan, a truck driver and his assistant were burned alive in a second attack, which targeted a single tanker in a restaurant parking lot, the Associated Press reported. The agency quoted police officer Mohammad Azam as saying "anti-state elements" were behind the attack. He did not name any particular group.

The Torkham pass, in the northwest, remained closed to NATO trucks Friday, one day after Pakistan blocked their passage in apparent retaliation for recent U.S. air incursions into Pakistan, including an airstrike Thursday that allegedly killed three Pakistani soldiers. The incidents drew a strong rebuke from Pakistan and deepened tensions with the United States, an ally.

Pakistan's ambassador to Belgium lodged a protest over the incursions with NATO on Friday, while Prime Minister Yousaf Raza Gillani told parliament that the government "will consider other options if there is interference in the sovereignty of our country."

Lt. Col. John Dorrian, a NATO spokesman in Afghanistan, said Friday that military officials have not yet confirmed that Pakistani border troops were killed in the NATO airstrike. He said the Pakistani border crossing closure has had minimal impact on NATO operations so far. "We're still bringing in a lot of stuff" via supply routes into the landlocked country from the north and south, he said. "There has not been an immediate impact."

A border security official in Pakistan's northwestern region said passenger vehicles and non-NATO supplies were being allowed to pass at Torkham on Friday. The Chaman border crossing remained open to all vehicles, and Pakistani media reported that the NATO trucks burned in Shikarpur were heading in that direction.

It is not uncommon for Islamist insurgents to attack NATO fuel trucks. But the incidents typically occur in the northwestern mountains, where several militant groups are based and wield influence. In the normally placid Chitral district near the Afghan border Thursday, police officials said 200 militants held a dozen policemen hostage and stole their weapons.

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