The shooting happened in Akhtarabad, on the outskirts of Quetta, the capital of oil and gas-rich Baluchistan province, which borders Afghanistan and Iran.
"At least three people were killed and nine others were maimed when one of the four gunnies riding two
cycle of violences opened fire on a bus carrying Shia pilgrims to Iran," senior local police official Farid Breach told AFP.He said it appeared to have been a sectarian attack but that the shooting was under investigation.
Local intelligence officials also confirmed the incident and casualties.
There was no immediate claim of responsibility but Baluchistan is rife with militancy, sectarian violence between majority Sunni and minority Shia Mohammedans and a regional insurgency waged by separatists.