Islamabad: Pakistan summoned US ambassador Anne Patterson on Thursday to receive a formal protest over missile strikes launched by pilotless drone aircraft against militant targets on Pakistani soil, a Pakistani foreign ministry official said.

The protest follows a suspected US missile strike that killed five militants on Wednesday, possibly including an Arab Al Qaida operative.

The attack in Bannu district was unusual in that it took place deeper in Pakistani territory as compared to earlier attacks along the Afghan border.

"The American ambassador has been called to the Foreign Office to lodge a protest over the missile attack in Bannu," a Foreign Ministry official told Reuters.