Three paramilitary soldiers and one policeman were killed when the gunmen opened fire on a Frontier Corps vehicle on the Fatima Jinnah road of Quetta.
Two civilians also sustained gunshot wounds and were admitted to a hospital.
"It appears to be a case of target killing and according to eye witnesses armed men on a motorcycle opened fire on the FC vehicle and the police constable who was on duty," he said.
Police said the attackers escaped unhurt from the spot.
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In three major suicide bomb attacks since August, over 150 persons have been killed and scores injured.
A suicide bomb attack was carried out at the entrance of the Civil hospital in Quetta in August in which around 70 persons were killed followed by a terrorist attack on the police training centre in the city in which two suicide bomber blew themselves up killing 64 police cadets and two army soldiers last month.
Last week, a suicide bomber blew himself up in the compound of the Shah Noorani shrine in the Khuzdar district, killing 54 devotees and security personnel.