A Shiite Muslim was ambushed as he drove through this once serene Himalayan tourist destination Saturday, sparking a rampage of sectarian violence and arson that left at least 11 people dead, including a family of six that was burned alive in its home.

Pakistan (search), a key ally in the U.S.-led war on terrorism, has suffered a wave of attacks blamed on Islamic militants in recent years, sometimes targeting top government officials and Westerners but more frequently hitting religious targets.

In October, a suicide bombing at a Shiite mosque killed 31 people in the eastern city of Sialkot. Six days later, a car bombing at a gathering of Sunni radicals in central Multan killed 40 people.

Authorities imposed an indefinite 24-hour curfew and army troops patrolled Gilgit to contain the violence, the second bout of unrest between rival Shiites and Sunnis there in six months.

Residents as far as 30 miles from the town said roads into Gilgit, home to about 25,000 people, had been blocked.

Police said hundreds of Shiites and Sunnis had clashed, setting fire to shops, homes and government buildings.

The Associated Press of Pakistan, the state news agency, reported the immolation deaths of the six family members. Geo television network said the father was a government forestry official.

Jamil Ahmed, regional chief administrator, said 11 people were killed in all. APP reported that 10 other people were injured.

The trouble started when unidentified gunmen shot and wounded a prominent Shiite cleric, Agha Ziauddin, as he traveled through the city in a car. His private security guards, one of whom was killed, fired back, killing at least one attacker. The motive for the attack on Ziauddin, who was hospitalized in stable condition, was not known.

Later, the local health chief, Sher Wali — a Sunni — was shot dead, Ahmed said.

Gilgit, a town set amid steep mountains, about 150 miles north of the capital, Islamabad, suffered sectarian unrest in June, when Shiites staged protests, demanding changes in Islamic textbooks used in state schools.

The protests spiraled into violence that claimed several lives. Authorities imposed a curfew for 13 days and had to airlift out some foreign tourists who were stranded in the city.

Although tensions had since eased, some schools have yet to reopen in the Gilgit area.

About 80 percent of Pakistan's 150 million people are Sunnis and 17 percent Shiites — although Shiites are in a majority in Gilgit and some other mountainous northern areas. Most of the Muslims live together peacefully, but small groups of militants on both sides stage attacks.

The schism between Sunnis and Shiites dates back to the 7th century over who was the true heir to the Prophet Mohammed.

Pakistani Information Minister Sheikh Rashid Ahmed condemned the killings in Gilgit, saying they were "the work of terrorists and such people have no religion."

Fearing the unrest could spread to other parts of the country, the Interior Ministry instructed authorities in each of Pakistan's four provinces to step up security for Muslim clerics and at places of worship.