Two pickup trucks carrying the troops back from a nighttime patrol came under fire in a mountainous region southwest of Baluchistan's capital, Quetta , a local police officer said.
Three troops from the Frontier Corps. paramilitary force were killed, the official said on condition of anonymity because he was not authorized to speak to the media.
An official at the Frontier Corps headquarters in Quetta, who also was not authorized to make media comments, confirmed that three soldiers died.
Pakistan's army is trying to stamp out a low-level insurgency in Baluchistan, a resource-rich but underdeveloped province bordering Afghanistan and Iran.
The region has seen protests and bomb attacks since the reported killing last week of Balach Marri, the leader of the Baluchistan Liberation Army guerrilla group.
Baluch nationalist groups are campaigning for greater autonomy for the region and more royalties for the extraction of its gas reserves.