An explosion ripped through a police truck on Wednesday to kill at least six people in Pakistan’s southwestern city of Quetta, police said.

The truck was carrying police recruits, four of whom were killed, along with two passers-by on the city's eastern outskirts, Quetta Police Chief Abdur Razzaq Cheema said.

“We can’t say whether it is a suicide blast,” he added. “Our teams are at the scene and investigating.” Television broadcast images of the burned-out remains of the vehicle.