The bomb, attached to a motorcycle, exploded near a security vehicle escorting school children, officials said. Sixteen people were wounded.
A Reuters reporter saw the corpses of three soldiers under the vehicle as it burned. There was no immediate claim of responsibility for the attack in Baluchistan, Pakistan's biggest but poorest province which borders Afghanistan and Iran and where several militant groups are active.
Ethnic Baluch separatists are waging an insurgency, demanding more autonomy and control over natural resources. Pro-Taliban militants are also active in the area and Sunni Muslim militants regularly carry out attacks on Baluchistan's Shi'ite minority.
(Reporting by Saleem Shahid; Writing by Michael Georgy)