Three people were killed when a pick-up laden with explosives blew up in the Pakistani city of Quetta, police said.
Police suspect the bomber was transporting explosives
The dead included two policemen and the driver of the pick-up, while three policemen and a child were injured, Qari Wahid, a police official, said.
It is not clear who was behind the latest explosion.
Quetta, capital of troubled Balochistan province, has been the target of frequent rocket and bomb attacks by tribal separatists in recent years.
The pick-up exploded outside the office of the provincial police chief.
But Mr Wahid said the police office was not a target. He also ruled out the possibility of a suicide attack.
Mr Wahid said the driver was possibly on his way to a more crowded part of the city when the explosives detonated accidentally.
Hours earlier, the police recovered explosives from a scooter parked in a major commercial area of the city.
Tribals groups have in recent years targeted gas plants, electricity lines and railway tracks in large parts of south-western Balochistan province.
They have been fighting for more autonomy and a greater share of the province's natural resources.
The army started an operation in different parts of the province more than a year ago to clear the area of rebels and establish military cantonments.
Violence has continued since August, when the military killed prominent tribal chief and politician, Nawab Akbar Bugti.