The remotely detonated bomb containing around 100 kilos (220 pounds) of explosives targeted a truck carrying members of a government paramilitary force on Thursday in the outskirts of Quetta, the capital of restive Baluchistan province.
Baluchistan, Pakistan's largest but most undeveloped province, is wracked by sectarian violence as well as a long-running insurgency waged by separatists, and attacks on security forces are common.
"At least 12 people have been killed, 11 of them were security personnel," senior police official Fayyaz Sumbal told AFP.
"The bomb was planted in rickshaw (tricycle). The target was a truck of Baluchistan Constabulary which was carrying the security personnel."
A further 11 people were wounded in the attack, he said. A bomb disposal officer confirmed the incident and death toll.
Baluchistan, which borders Afghanistan and Iran, has significant reserves of gas and other resources, but development has been limited by the volatile security situation.
Ten days ago the provincial police chief narrowly escaped a suicide car bomb attack outside his home in Quetta that killed at least six people and wounded 46 others.