Major General Roy Galido, commander of the Filipinos Army's Sixth Infantry Division, said the bomb, believed to be an improvised explosive device, went off while traveling southwest from Kidapawan City to Tacurong City on Mindanao island.
Galido added that the military has coordinated with the provincial police to investigate whether the attack was part of an extortion activity of criminal groups in the area.
The bus company has been getting bomb threats, Galido said.
No group has claimed responsibility for the attack./.