Zamboanga City, Philippines  - Three police officers and two security aides of a governor were wounded Wednesday in a bomb attack in the southern Philippines, a regional police chief said.

Chief Superintendent Bensali Jarabani said the explosion occurred a few metres from provincial capitol of Sulu province on Jolo island, 1,000 kilometres south of Manila.

Jarabani said the explosion hit the convoy of vehicles of Sulu Governor Abdusakur Tan, who was on his way home in downtown Jolo.

Investigators were still trying to determine who was behind the attack and the make of the bomb which was placed on a parked motorcycle.

Tan was unharmed in the attack.

Thousands of government forces were conducting operations on Jolo to rescue Eugenio Vagni, a 62-year-old International Committee of the Red Cross (ICRC) employee held captive by Muslim Abu Sayyaf rebels.

Vagni was abducted along with fellow ICRC workers Swiss Andreas Notter and Filipino Mary Jean Lacaba on January 15.

Notter and Lacaba have been released by the guerrillas and only Vagni, who is reportedly suffering from an hernia injury, remains in captivity.(dpa)