By Faisal Aziz
KARACHI (Reuters) - Suspected militants in Pakistan set fire to tankers carrying fuel for NATO troops in Afghanistan on Friday, officials said, a day after three soldiers were killed in a cross-border NATO air strike.
Pakistani authorities, angered by repeated incursions by NATO helicopters over the past week, have blocked a supply route for the troops in Afghanistan.
Senior local officials said "extremists" are believed to have carried out the attack on the tankers in the southern town of Shikarpur early on Friday.
About 12 people, with their faces covered, opened fire with small arms in the air to scare away the drivers and then torched some 30 vehicles.
Three Pakistani soldiers were killed and three wounded on Thursday in two cross-border strikes by NATO forces chasing militants in Pakistan's northwestern Kurram region.
It was the third cross-border incident in a week, the Pakistan military said. NATO said the helicopters briefly crossed into Pakistan airspace after coming under fire from people there.
Hours later, Pakistani authorities halted tankers carrying supplies for the NATO forces passing through the Khyber tribal region on the Afghan border.
Pakistan is a crucial 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 United States has already stepped up missile strikes by its pilotless drone aircraft on militant targets inside Pakistan.
A senior Pakistani intelligence official said border incursions were a "red line" and could lead to a "total snapping of relations."
About half of all cargo for NATO forces in Afghanistan travels through Pakistan, most of it via two main border crossings: Chaman and Torkham.
Another third flows into Afghanistan through the northern distribution network across Kazakhstan and Uzbekistan. Sensitive gear like ammunition, weapons and critical equipment is flown in.
(Additional reporting by Hamid Sheikh; Writing by Zeeshan Haider; Editing by Michael Georgy and Sanjeev Miglani)