Gunmen opened fire on vehicles carrying Shiite Muslims in Pakistan's restive northwest on Thursday, killing at least 38 people, including six women, and wounding 20 others in one of the region's deadliest such attacks in recent years, police said. The attack happened in Kurram, a district in Khyber Pakhtunkhwa province where sectarian clashes between majority Sunni Muslims and minority Shiites have killed dozens of people in recent months. No one immediately claimed responsibility for the latest attack.

It came a week after authorities reopened a key highway in the region that had been closed for weeks following deadly clashes. Local police official Azmat Ali said several vehicles were traveling in a convoy from the city of Parachinar to Peshawar, the capital of Khyber Pakhtunkhwa, when gunmen opened fire. He said at least 10 passengers were in critical condition at a hospital.

Interior Minister Mohsin Naqvi said at least 38 people were killed in the “terrorist attack." Prime Minister Shehbaz Sharif and President Asif Ali Zardari condemned the attack, and Sharif said those behind the killing of innocent civilians will not go unpunished. A witness, 35-year-old Mir Hussain, said he saw four gunmen emerge from a vehicle and open fire on buses and cars.

“I think other people were also firing at the convoy of vehicles from nearby open farm field,” he said. “The firing continued for about 40 minutes.” He said he hid until the attackers fled.

“I heard cries of women, and.