Tankers carrying supplies for NATO troops in Afghanistan have been
set on fire by unidentified assailants in the Pakistani town of
Shikarpur in Sindh province, officials say.

The incident on Friday came a day after Pakistani authorities blocked a supply route for NATO troops, angered by the killing of three Pakistani soldiers in airstrikes by NATO helicopters.

"The attackers fired with small arms on tankers and fled away. No one
was hurt," an official of the paramilitary Rangers force told the
Reuters news agency.

The official, who declined to be named, said about 10 assailants attacked up to 25 to 30 tankers early in the morning.
   
Efforts were underway to put out the fire, a police official, Mir Hazar Chandio, said.

The
supply route remained blocked on Friday and lorry was allowed to enter
Afghanistan for the second consecutive day, an administrative official
said.

"Trucks carrying fuel and other goods for NATO are still not allowed
to enter Afghanistan," the official, speaking from Torkham, the main
crossing border between Pakistan and Afghanistan, told the AFP news
agency by telephone.

Aviation fuel
   
The
three Pakistani soldiers were killed on Thursday in two cross-border
strikes as NATO troops were chasing anti-government fighters in
Pakistan's northwestern Kurram region.
   
Hours later, Pakistani
authorities halted tankers carrying supplies for the NATO forces
passing through the Khyber tribal region on the Afghan border.

Al
Jazeera's Kamal Hyder, reporting from the the Pakistani capital,
Islamabad, said the blocked route is a "very crucial part of the supply
chain because most of the aviation fuel [for NATO aircraft] goes through
Pakistan".

"It's that aviation fuel that's used in combat missions inside Afghanistan," he said.

Our
correspondent said previous attacks on NATO convoys have taken place in
Balochestan or the province of the North-West Frontier and that
Friday's attack in the southern province of Sindh was a rare occurrence.
   
Pakistan
is a key ally for the United States in its efforts to stabilize
Afghanistan, but analysts say border incursions and disruptions in NATO
supplies underline growing tensions in the relationship.
   
The bulk of supplies for the troops in Afghanistan goes through Pakistan.