Islamabad  - Suspected Taliban militants opened fire on a group of students in Pakistan's north-western tribal region on Tuesday, killing at least four of them, officials said.

The students came under attack as they travelled on foot to their school in the Utman Khel area of lawless Orakzai district, an official in the administration told the German Press Agency dpa by phone.

"Four students were fatally shot while three others suffered bullet wounds," Asmatullah said.

Authorities said the militants, who largely belong to the majority Sunni Muslim community, attacked the school-goers probably as part of their ethnic campaign. All those killed and injured were Shiites.

Aaj News television channel reported that the militants wanted to kidnap the students, and managed to seize at least two.

The assault triggered a gunfight between the militants and a pro-government militia, which was raised to resist the Taliban insurgency. One attacker was killed and three others injured in that clash.

Taliban fighters in Orakzai are commanded by Hakeemullah Mehsud, who recently succeeded the Pakistani Taliban chief Baitullah Mehsud after his death in a US missile strike on his stronghold of South Waziristan early last month.

Orakzai is the only district in Pakistan's troubled tribal region which does not share a border with neighbouring Afghanistan.

Orakzai used to be relatively peaceful but violence surged during the last two years as militants from nearby areas infiltrated the district to escape ongoing military operations.

Elsewhere, four paramilitary soldiers were injured in what was believed to be a hand-grenade attack in the nearby Khyber tribal district.

Security forces launched an offensive against Islamist insurgents in Khyber last week, killing at least 140 rebels and arresting nearly 130 others in continued fighting. Two dozen militant hideouts and scores of houses were also destroyed.

A spokesman for the Frontier Corps paramilitary force said the operation would continue until it achieved the "complete elimination" of the militants, who are involved in attacks on troops and kidnappings for ransom.

Khyber serves as the key land route to haul fuel and military equipment for NATO forces fighting the Taliban in landlocked Afghanistan. Militants regularly attack the NATO-bound trucks, temporarily suspending the supplies. (dpa)