The death toll from Pakistani air strikes on militant hideouts in a northwestern tribal area on Wednesday rose to 55, with reports of some civilian deaths, security officials said.

Pakistani jet fighters on Tuesday targeted militants preparing for imminent suicide attacks and destroyed their bases in the lawless Khyber tribal district, which borders Afghanistan, security officials said.

"Militants were using civilians and their families as human shields and there could be some civilian casualties but we do not know how many," a senior security official told AFP, confirming the new toll.

Two military and an intelligence official also confirmed the incident in the Tirah valley as well as the death toll. "At least 12 civilians were killed when jets dropped shells on a convoy," a local government official told AFP, requesting anonymity.

In April, Pakistan Army chief Gen. Ashfaq Kayani made a rare public apology for the deaths of some 60 civilians, also in Tirah valley, during military operations and issued orders to avoid further incidents.

Security officials said the air strikes destroyed militant hideouts, a training centre, an illegal FM radio station and eight vehicles prepared for suicide attack in Peshawar, the capital of Khyber Pakhtunkhwa province.

A senior military official in Peshawar said that he had no information about civilian casualties in the air strikes. The militants belonged to the Lashkar-e-Islam group and included fighters who fled last year's offensive by the Pakistani military in the northwestern Swat valley, the security official said.

Lashkar-e-Islam, which means Army of Islam, is a domestic Islamist group with ties to the Taliban that has caused unrest in the Khyber region, including attacks on NATO supply vehicles travelling through the area.

Khyber is on the main NATO land supply route through Pakistan into Afghanistan, where almost 150,000 foreign forces are battling to reverse an escalating Taliban insurgency, now in its ninth year.

The district neighbours the northwestern city of Peshawar, which is increasingly the target of Taliban and Al Qaeda-linked bomb attacks. US officials consider northwest Pakistan a haven for Al Qaeda and Taliban militants who fled the 2001 US-led invasion of Afghanistan to regroup and launch attacks on foreign troops across the border.

Bombs and attacks blamed on Taliban and Al Qaeda-linked militants have killed more than 3,500 people across nuclear-armed Pakistan since government troops besieged a radical mosque in Islamabad in July 2007.

Pakistan has launched several operations in the past two years in Khyber to flush out the fighters. In April 2009, Pakistan launched a major offensive in the province's northern districts of Buner and Lower Dir, then advanced through the valley of Swat, with heavy fighting that displaced an estimated two million people.

The military declared the region back under army control last summer, but tentative efforts to kickstart development in the area have been set back by the castastrophic August floods that swept away bridges and cut off the area.

Another anti-militant military operation is under way in the northwest tribal district of South Waziristan, which is also regularly targeted by US drones hunting Taliban and Al Qaeda linked militants.