QUETTA, Pakistan — Pakistani police say gunmen have killed four women in an attack on a bus carrying members of the country’s Shiite minority in the southwestern city of Quetta.

Police spokesman Shahzada Farhat says another woman and a man were wounded in Tuesday’s attack. Farhat says the attackers fled the scene on motorcycles and that police have launched a search operation.

No one claimed the attack, but the Lashker-e-Jhangvi group has claimed similar attacks on Shiites in the past. Sunni Muslim extremists view Shiites as apostates deserving of death.

Pakistani authorities had heightened security across the country to protect Shiites during the month of Muharram, when they mourn the 7th century martyrdom of the grandson of the Prophet Muhammad.