Nato supply lorries set ablaze by gunmen in Pakistan
Militants in Pakistan have destroyed at least 40 tankers carrying fuel for Nato in two separate attacks, police say.
The first attack hit a depot near Quetta while the second set ablaze a convoy in Nowshera, in the north-west.
Attacks on tankers have soared since Pakistan shut one of the main routes into Afghanistan over the deaths of several soldiers in a Nato raid.
The US and Nato have apologised for the helicopter attack last week which killed at least two Pakistani soldiers.
Nato admitted two of its helicopters entered Pakistan on 30 September and killed two border guards, mistaking them for militants after they fired shots.
Pakistan says three soldiers were killed.
The attack infuriated public opinion in Pakistan and led to anti-Nato demonstrations.
The US ambassador to Pakistan, Anne Patterson, described it as a "terrible accident" and said she was offering an apology on behalf of the American people.
"We extend our deepest apology to Pakistan and the families of the Frontier Scouts who were killed and injured," she said.
Nato's Gen David Petraeus also apologised and vowed to work to stop similar incidents happening in the future.
The Pakistani authorities closed the Torkham crossing in the north-west after the incident.
The move has stalled hundreds of lorries carrying Nato supplies bound for Afghanistan, making them easy targets for militants.
In the Nowshera attack, gunmen raided a convoy parked along the road, setting ablaze some 20 fuel tankers.
Police said they did not know if anyone had been killed.
Hours earlier on Wednesday, hundreds of miles to the south, gunmen struck a depot near Quetta where dozens of fuel tankers were parked.
Police said up to 14 gunmen in two pick-up trucks opened fire on the tankers, killing one driver.
BBC Urdu's Ayub Tareen rushed to the scene after the ambush and was lucky to escape with scratches when one of the blazing fuel tankers exploded.
The Pakistani Taliban said they carried out both raids, the fourth and fifth such attacks in the past week.
'Avoiding the Taliban'
Nato officials say the attacks have not had any significant impact on operations.
A senior spokesman for Nato-led Isaf forces in Afghanistan, Gen Josef Blotz, told the BBC there were "plenty of supplies and stocks within Afghanistan already".
The Chaman crossing in Balochistan remains open, but this is not as convenient for supplies bound for Kabul.
Supplies can also be brought into northern Afghanistan via Uzbekistan and Tajikistan.
The shutting of the border post has strained relations between Pakistan and the US.
Those ties could be further strained by a White House assessment that paints a critical picture of Pakistan's willingness and ability to tackle Taliban and al-Qaeda militants operating in North Waziristan, near the border with Afghanistan.
The report said Pakistan's military stayed close to the main roads, avoiding "military engagements that would put it in direct conflict with Afghan Taliban or al-Qaeda forces in North Waziristan".
This was "as much a political choice" as a question of military ability, the report said.