ISLAMABAD: Pakistan has upgraded its air defence system on the Afghan border to make it capable of shooting down aircraft, after Nato strikes killed 24 Pakistani soldiers, a security official told AFP on Friday.

“Now we have a fully equipped air defence system on the Afghan border. It has the capability to trace and detect any aircraft,” the official in Peshawar told AFP by telephone.

The official, who spoke on condition of anonymity because he was not authorised to speak to the media, said the step had been taken to avert air incursions from Afghanistan and to respond to any future air strikes.

“The system has also been upgraded to immediately respond after detecting any aircraft or helicopter and to shoot it down,” he added.

Pakistan shut its border to Nato supply convoys on November 26, the same day as the deadliest single cross-border attack of the 10-year war in Afghanistan.

The government also ordered the United States to leave the Shamsi air base in the southwest, widely reported as a hub in the covert CIA drone war against the Taliban and Al-Qaeda in Pakistan's border area with Afghanistan.

Pakistan gave tacit support to the programme, but no US drone strike has been reported on Pakistani soil since November 17.

The November 26 attacks brought the fragile Pakistani-US alliance to a fresh low, already reeling from an American stealth raid that killed Al-Qaeda leader Osama bin Laden in Abbottabad on May 2.

It was after that raid, conducted by US Navy SEALs who flew in from Afghanistan, that Pakistan first upgraded its defence systems on the border.

US President Barack Obama has expressed condolences over the November 26 border deaths, insisting it was not a “deliberate attack” by Nato as claimed by the Pakistani army.