The explosives were planted under a car parked on Saryab Road on the outskirts of Quetta, the capital of the province of Baluchistan, which borders Afghanistan and Iran.
Local police said the explosion on May 1 apparently targeted a Frontier Corps paramilitary convoy.
RFE/RL's Radio Mashaal reports that the Taliban has claimed responsibility for the attack.
On April 29, the decapitated body of a British aid worker, Khalil Dale, was found in Quetta, almost four months after he was snatched by masked gunmen in the city.
He was the third Westerner kidnapped and beheaded in Pakistan since 2002.