Philippine National Police (PNP) city director Superintendent Rogelio Nuñeza said they have several suspects in the grenade attack on the market area in Barangay Pala-o.
"This is terrorism," Nuñeza said while refusing to identify the suspects.
No group has claimed responsibility for the attack, which left three young men killed and 32 wounded, seven of whom are in critical condition.
Nuñeza identified two of the fatalities as Jerry Alido, 21, of Pagadian City and Rene Bantilan, 19, of Tubod, Lanao del Norte. Both men died on the spot while another expired while being treated at a local hospital.
In the critical list are couple Justiniano and Eliza Capadizo, Nonita Lagudas, Quiney John Pomipic, Reynaldo Revales, Rey Villanes and Rico Watiman.
Being treated for shrapnel injuries are Erwin Aligno, Florenza Ardenia, Azel Boransing, Ariel Cadiano, Ramil Calunod, Leo Cayros, Dondon Falcon, Ramil Falcon, Helen Gimeno, Gerardo Gisilisin,
Julius Lagudas, Mary Grace Lagudas, Salome Madrid, Pablita Magdale, Alicia Pomopic, Sonia Revales, Elvis Sisnot, Orlando Sistona, Veronica Teanco, Annie Togonon, Rosanna Villanea and Rosa Visitacion.
An initial police investigation showed that shortly before 7 p.m., two men riding a motorcycle lobbed a fragmentation grenade at the entrance of the Apollo Electrical Supply store on Aguinaldo Extension street.
Police said they knew of no connection between the attack and the Abu Sayyaf hostage crisis in Basilan. – With Roel Pareño