Islamabad, Pakistan (CNN) -- A bomb blast struck a bus in the restive Pakistani province of Balochistan on Monday, killing six people and wounding 50 others, a senior government official said.
The explosive device, planted on a motorbike parked by the side of the road, went off as the bus drove past, said Irfan Shah Gharsheen, an official from Mastung District in Balochistan, a southwestern province riven by sectarian tensions and militant violence.
The target of the attack was a convey of vehicles carrying Shiite Muslims, Gharsheen said. The explosion took place in the area of Gen in Mastung, 90 kilometers southeast of the provincial capital of Quetta.
Shiites have suffered frequent attacks in Balochistan in recent years. In March, gunmen riding motorbikes shot and killed five Shiites traveling in a van near Quetta.
Balochistan is Pakistan's largest province and lies along the border with Iran and Afghanistan.