ISLAMABAD: An apparent U.S. missile attack destroyed an Islamic school in an al-Qaida stronghold of northwestern Pakistan on Saturday, killing 12 people including two suspected foreign militants, officials said.

The strike came as Pakistan's army prepared to assail Taliban militants entrenched in the main town of the Swat Valley, from where nearly a million civilians have fled a military offensive against Taliban guerrillas.

American forces have maintained a bombardment of militant targets in the lawless Pakistani regions bordering Afghanistan while pressing Islamabad to tackle Taliban-held regions further inland.

Pakistani officials said several missiles hit the school and a nearby vehicle Saturday morning in Mir Ali, a town in the North Waziristan tribal region.

Two intelligence officials, citing reports from agents in the field, said at least 12 people were killed, including two foreign militants, and dozens more were wounded.

The exact identity of the victims was not immediately clear, the officials said. They spoke on condition of anonymity because they were not authorized to speak publicly to the media.

President Barack Obama has identified the elimination of militant sanctuaries in Pakistan as critical if America is to eliminate al-Qaida and turn around its faltering war effort in Afghanistan. Pakistan's border region is considered the likely hiding place of al-Qaida chief Osama bin Laden.

Using unmanned aircraft, American forces have carried out dozens of missile attacks in northwestern Pakistan over the past year. U.S. officials rarely confirm the attacks, but say they have killed a string of al-Qaida commanders.

Pakistan's government has publicly protested against the tactic, arguing that it kills too many civilians and undermines its efforts to turn tribal leaders away from hard-liners.

The Pakistan army this week rejected media reports that it was jointly controlling missions by U.S. drones over Pakistani territory. The civilian government has asked Washington to add drones to its latest military aid package.

Pakistan's Western backers have also expressed concern that Taliban militants advancing from the Swat Valley toward the Islamabad pose a growing threat to the stability of the nuclear-armed nation.

To push them back, the army last month launched an offensive in the Swat area that it claims has killed more than 800 militants as well as dozens of troops.

On Friday, the army lifted its curfew on the main town of Mingora to allow thousands more to join the more than 900,000 civilians who have already fled the fighting. About 90,000 are housed in sweltering camps south of the war zone.

The army has said it hopes all Mingora's population will flee before it begins "street-to-street" combat in the town. Residents have reported militants laying mines and digging trenches to counter an attack.

The military claimed Friday that militants were shaving their beards and mingling with civilians in order to escape and appealed to refugees to point them out at checkpoints ringing the town.

The offensive is a key test of Pakistan's will and ability to defeat Islamist militants. The Swat Taliban fought the army to a stalemate in the valley last year, prompting the country's politicians to strike a peace deal that collapsed last month.

The military says it is advancing slowly in Swat to limit civilian casualties. Public opinion appears to support the offensive, but the mood could quickly turn against the pro-Western government if the fighting drags on and civilian hardship mounts.