At least two policemen and as many civilians were injured in an explosion on Quetta's Spinny Road on Monday, police sources said.
The target of the blast, carried out using an improvised explosive device (IED), was a police mobile, the sources added.
The explosives were planted in a motorcycle parked on the roadside and were detonated when the police vehicle passed by on the road. As a result, two policemen and two civilians sustained injuries.
TV footage showed the blast left the police mobile partially damaged while at least one car parked nearby was completely damaged.
The injured were shifted to Quetta Civil Hospital's trauma centre, where an emergency was imposed.
Police and Frontier Corps personnel rushed to the site as an investigation into the incident went underway.
This is the second blast targeting security forces in the span of a week in Balochistan's capital. On Tuesday evening, a Rapid Response Force sniper was martyred and 10 others — five security personnel and as many civilians — were injured in a bomb blast that rocked Quetta's busy Double Road area.
Earlier this month, opposition lawmakers in the Balochistan Assembly had demanded setting up of a fact-finding committee to probe increasing terrorist attacks in the province.