A security official said that six security men were injured in the blast, which appeared to be a suicide attack, targeting a Frontier Corps (FC) post in the Darvaish Belili area of provincial capital Quetta.
"We are still investigating the incident and the exact nature of bombing will be determined after the report by bomb disposal experts," he said on anonymity.
The injured were shifted to Civil Hospital Quetta for treatment, as forces started search operation in the area.
It was second attack at the security forces in Quetta during the day, as two policemen were killed earlier today when gunmen opened indiscriminate firing at vehicle of Deputy Superintendent Police Hameedullah Dasti on Samungli Road of the city.