"We have temporarily suspended the movement of buses on the highway until the security situation improves," a senior official of the provincial government told Reuters.
The 700 km (430 mile) highway connecting the Quetta and Iran, has seen dozens of suicide and roadside bomb and gun attacks on pilgrims in recent years.
The route is popular among Shia pilgrims, who travel via buses into neighbouring Iran and then onto Iraq and the holy sites of Karbala.
In the latest attack on Tuesday, a suicide bomber had driven his car into a bus killing 27 pilgrims. The attacked prompted hundreds of Hazaras, who inhabit Quetta, to take to the streets to protest against the violence.
"No place is safe for us. There is no alternate road. We have to travel through this 'bloody highway' each time we go on a pilgrimage," said Mohammad Ismail Changazi, one protester.
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