Police said the victims, Arpa Mamalangcop, a Maranaw, and Gil Navarra were just meters away from the spot where the grenade landed.
The two are now confined in a private hospital here.
PPA officials still have no clues on the motive behind the grenade attack.
The grenade thrower casually pulled over near the supposedly tightly guarded gate of the city wharf, pulled out a Mark II grenade from his pocket, removed its pin, and tossed it into the PPA office.
Cotabato City Mayor Muslimin Sema said the PPA office has been active in helping the city government enforce security measures to protect the wharf from criminals and terrorists. — John Unson