Gunmen opened fire on a convoy of passenger vehicles carrying Shiite Muslim civilians in restive northwest Pakistan on Thursday, killing at least 50 people and wounding 20 others in one of the deadliest such attacks in recent years in the region, police said.

The attack happened in Kurram, a district in the northwestern Khyber Pakhtunkhwa province where sectarian clashes between majority Sunni Muslims and minority Shiites have killed dozens of people in recent months.