Troops were escorting a group of aid workers and journalists to the inaugural ceremony of a rebuilt government school in Maidan town in Lower Dir district when the blast hit the convoy.

The explosion took place near another school for girls in Koto, about 8 kilometers from Lower Dirs main town of Timergara.

Three foreigners, three schoolgirls, one (Pakistani) soldier and a private security guard were killed in the blast, district police chief Mumtaz Zareen said.

The US embassy in Islamabad identified the three foreign victims as US soldiers who were training Pakistans paramilitary Frontier Corps, and said that two more were injured.

A statement from the US mission condemned the vicious terrorist bombing.

The statement said the US soldiers had gone to the area to attend the inauguration ceremony of a school for girls that had recently been renovated with US humanitarian assistance.

US troops have been training the Frontier Corps since 2007 under a program to improve the efficiency of the poorly equipped and under-trained force in north-western Pakistan.

More than 75 people, mostly schoolgirls, were wounded in the explosion Wednesday. Hospital authorities said they feared the death toll might increase, because six of the victims were in critical condition.

Local police said explosives experts suspected it was a car bomb attack carried out by a suicide bomber.

The blast destroyed three vehicles in the convoy. The school building collapsed, trapping students in the debris.

There was smoke and dust all over after the blast and people were screaming for help, said local journalist Haroon Rashid, who was travelling with the convoy.

Television footage showed people sifting through the rubble for survivors. The explosion left a crater around a metre deep.

Pakistani security forces carried out a major offensive in Lower Dir and nearby districts last spring to dislodge the Taliban fighters concentrated in Swat valley.

Although the government forces have gained control over much of the area, Taliban fighters remain in mountain hideouts.

Wednesdays attack showed that the militants are still capable of conducting deadly assaults on the military in Lower Dir and adjoining districts.

The district is also located close to Pakistans lawless tribal belt, a known sanctuary of al-Qaeda and Taliban militants who fled the US-led invasion of Afghanistan after the 9/11 terrorist attacks.

US forces have intensified airstrikes against suspected militant hideouts and training camps in the North and South Waziristan tribal districts since the December 30 suicide attack on a US base in Afghanistan. Five intelligence agents and two private contractors were killed in the attack.

A barrage of missile strikes launched Tuesday night by nine pilotless aircraft in different villages killed at least 31 insurgents. Up to 18 missiles fired from the drones hit mud compounds, bunkers and vehicles, the military said.

The region is a stronghold of Pakistani Taliban leader Hafiz Gul Bahadur, who allegedly sends militant reinforcements to Afghanistan.

A US drone was shot down by militants in the same area January 24.

Washington usually refused to confirm or deny the drone strikes, which are officially condemned by Pakistan as a violation of its territorial integrity.