According to sources, the forces vehicle was on its way from the Khajuri check-post to Khwar check-post when the blast occurred.
Security forces sealed the area and started a search operation following the incident.
Earlier, at least seven police personnel were martyred and 22 people were injured in an explosion in the Sariab Mill area on the Quetta-Sibbi Road.
According to security sources, a roadside bomb exploded just as a police vehicle carrying 35 policemen passed the area. However, the nature of the blast has yet to be ascertained.
Civil Hospital Quetta Spokesperson Wasim Baig confirmed seven casualties and said that eight injured had been brought to the medical facility where emergency has been imposed.