At least three agents of Pakistani's Inter-Services Intelligence (ISI) have been killed after six armed men ambushed a military vehicle on patrol in northwestern Pakistan, police say.

Two other people were wounded in Wednesday's ambush in Sarai Khan on the outskirts of Bannu city by the assailants believed to be pro-Taliban fighters, police said.

Sajjad Khan, the local police chief, told the AFP news agency the attackers opened fire on the army pickup truck from both sides of the road.

Security officials confirmed the attack and casualties.

It came a day after Taliban ambushed a school bus on the outskirts of the northwestern city of Peshawar, killing four children and the van driver.

At least 12 boys, two girls and two female teachers were wounded in the attack, said Qayyum Khan, a police officer.

The children studied at an elite English-language school of a type reviled by hardline fighters who oppose what they see as Western-imported, secular education.

Bannu, where the ambush happened, is located close to Pakistan's lawless tribal belt, which the United States considers the most dangerous region on earth and an al-Qaeda headquarters.

Source: Agencies