A senior Pakistani military officer said a NATO air strike that killed 24 Pakistani troops on the border with Afghanistan last month was pre-planned, newspapers reported Friday, comments likely to fuel tension with the United States.

Maj. Gen. Ashfaq Nadeem, director general of military operations, also said Pakistan, a strategic U.S. ally, would deploy an air defense system along the border to prevent such attacks, the newspapers said.

The newspapers said he made the remarks to a Senate committee on defence on Thursday. Military officials were not immediately available to comment.

The Daily Times said Nadeem described the attack as a plot while another newspaper quoted him as saying it was a pre-planned conspiracy against Pakistan.

We can expect more attacks from our supposed allies, Nadeem was quoted as saying during his briefing, The Express Tribune reported.

U.S. and Pakistani officials have offered differing initial accounts of what happened.

Pakistan said the attack was unprovoked, with officials calling it an act of blatant aggression -- an accusation the United States has rejected.

Two U.S. officials told Reuters that preliminary information from the ongoing investigation indicated Pakistani officials at a border coordination centre had cleared the air strike, unaware they had troops in the area.

Nadeem ruled out the possibility that NATO forces may have thought they were firing on militants, who often move across the porous frontier and attack Western troops.

One newspaper reported that he told the Senate committee that militants do not leave themselves exposed on mountain tops, like the ones where the Pakistani border posts were located.

Pakistan responded to the attack by suspending supply routes to NATO forces in Afghanistan.

Idle drivers of trucks carrying fuel and other supplies to the neighbouring country fear being attacked by Pakistani Taliban militants who oppose cooperation with NATO.

Militants fired a rocket-propelled grenade at such trucks in the southwestern city of Quetta in Baluchistan province on Thursday night, setting fire to 29 vehicles, police officials said.

Washington, which sees Pakistan as critical to its efforts to stabilise Afghanistan ahead of a combat troop pullout in 2014, has tried to sooth fury over the NATO incident.

President Barack Obama called Pakistan's president to offer condolences over the strike that provoked a crisis in relations between the two countries. He stopped short of a formal apology.

Pakistan boycotted an international conference in Germany on the future of Afghanistan because of the NATO attack.

U.S.-Pakistani ties were already frayed after the secret U.S. raid in May that killed al Qaeda leader Osama bin Laden.

(Writing by Michael Georgy; Editing by Nick Macfie)