"At least three people were killed and nine others were wounded when one of the four gunmen riding two motorbikes opened fire on a bus carrying Shia pilgrims to Iran," senior local police official Farid Breach told AFP.
He said it appeared to be a sectarian attack but that the shooting was under investigation.
The bus was on its way from Taftaan to Quetta.
Local intelligence officials also confirmed the incident and casualties.
There was no immediate claim of responsibility but Baluchistan is rife with Islamist militancy, sectarian violence between majority Sunni and minority Shia Muslims and a regional insurgency waged by separatists.
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