QUETTA, Pakistan—A government official says a motorcycle bomb has ripped through a passenger bus in southwest Pakistan, killing three people and injuring 40 others.

Irfan Shah said the bomb Monday targeted Shiite pilgrims travelling to Iran but hit a local passenger bus instead.

The attack took place in Mastung district in Baluchistan province.

Sunni extremists have carried out scores of attacks on Shiites in Baluchistan in recent years, often as they travel to Shiite-dominated Iran for pilgrimages.