Officials say 10 inmates, including two alleged Chinese drug criminals, died in a suspected grenade blast that rocked a Philippine jail.

Senior Inspector Xavier Solda, spokesman of the Bureau of Jail Management and Penology, said Friday initial investigation showed the inmates had sought to talk with the warden of Paranaque City jail in metropolitan Manila upon learning they would be transferred to another facility. The warden was seriously injured in Thursday night's explosion.

Solda says eight of the inmates killed in the blast were facing drug cases, including two Chinese nationals. Two others were facing cases of robbery with homicide.

Solda says investigators are looking at whether the blast was part of an escape attempt. But he says they are waiting to get details from the warden.