ISLAMABAD, Pakistan — Pakistani forces launched a dawn strike with missile-firing helicopters against a religious school yesterday that killed at least 80 suspected militants.

It sparked protests by Islamist groups, as Prince Charles and the Duchess of Cornwall started the first full day of their visit to Pakistan.

A Pakistan army spokesman said that the madrassa, or religious school, near the town of Khar in the Bajaur tribal agency in the Northwest Frontier Province was being used as a “militant training camp.”

“We received confirmed intelligence reports that 70–80 militants were hiding in a madrassa used as a terrorist training facility, which was destroyed by an army strike, led by helicopters,” the chief army spokesman, Major General Shaukat Sultan, said.

He added: “These militants were involved in actions inside Pakistan and probably in Afghanistan.”

General Sultan said that those in charge of the madrassa had refused warnings by the military in recent weeks to close it down. The leader of the madrassa, a radical cleric called Maulana Liaqat Ullah Hussain, was among the dead.

Residents said that they had seen three or four army helicopters flying over the village of Chenagai at around 5 a.m. The blast leveled the compound, tearing mattresses and scattering Islamic books, including copies of the Koran, according to a local reporter.

Witnesses claimed that the dead were not militants but included young students and teachers. Several hours after the attack, the bodies of 20 dead tribesmen were lined in a field near the madrassa before a burial attended by thousands of angry locals.

Among those said to have been killed was Liaquat Hussain, a Pakistani cleric and associate of Osama bin Laden’s deputy, Ayman al-Zawahiri. He is reported to have sheltered Al Qaeda operatives in the past.

Another associate of Zawahiri, Faqir Mohammed, was believed to have been in the madrassa and left 30 minutes before the strike, a Pakistani intelligence official claimed.

The death total is the highest for a single military operation targeting suspected Islamic militants in Pakistan, who cross the border into Afghanistan to join the Taliban insurgency against NATO-led and Afghan forces.

It provoked an angry backlash from Islamic groups.

Thousands of protesters took to the streets in Khar, Bajaur’s main town, where they shouted anti-Western slogans. There were also protests in Pakistan’s largest city, Karachi. Islamic parties called for further protests in the province today.