Islamabad, Pakistan (CNN) -- A truck laden with explosives rammed into the wall of a paramilitary complex in Pakistan on Thursday and detonated, a military spokesman said.
The blast in Karachi injured 21 -- three critically -- and damaged the wall of a Rangers housing complex, said Maj. Bilal Farooq. No deaths were reported.
Farooq condemned the attack as a "cowardly act."
The truck had more than 220 pounds (100 kilograms) of explosive material, said Karachi police spokesman Javed Odho.
The Rangers are a paramilitary force in the Pakistani army often assigned to security detail in conflict regions.