Philippine officials say a bomb packed with nails for more lethal effect has exploded in a massage parlor in the country's south, killing one person and leaving at least eight others wounded.

Philippine police say two of the victims of late Thursday's blast in the port city of Zamboanga were in critical condition in a hospital. No group immediately claimed responsibility for the night-time attack, which damaged the shop and nearby businesses.

Police say investigators are still trying to determine the identity of the attackers. Zamboanga, a bustling city that's a gateway to many urban centers in the south, has come under bomb attacks by Abu Sayyaf militants in the past.