Zamboanga City, Philippines  - Two people were killed when an improvised bomb exploded outside a fast-food restaurant in a southern Philippine city, a provincial police chief said Saturday.

Senior Superintendent Salik Macapantar said eight more people were injured in the explosion that occurred late Friday in Isabela City in Basilan province, 900 kilometres south of Manila.

Macapantar said a man and a woman passing by when the bomb exploded had died.

"They were killed on the spot," he said.

Investigators suspected Muslim Abu Sayyaf rebels trying to divert the attention of government operations against them.

The al-Qaeda-linked guerrillas are still holding captive six public school teachers, one Sri-Lankan peace advocate, and an employee of a local lending firm. Last week, the guerrillas released a 9-year-old boy after the family paid an undetermined amount of ransom.

A separate group of Abu Sayyaf rebels are holding captive two foreign International Committee of the Red Cross staff on nearby Jolo Island. (dpa)