Two improvised bombs exploded on Friday in a southern Philippine city, but no injuries were reported, a police report said.
The two explosions occurred before dawn in downtown Zamboanga City, 870 km south of Manila, according to city police chief Edwin de Ocampo.
Senior Superintendent De Ocampo said the first blast occurred in a street near the city's business centre while the second bomb went off at a public plaza near the city hall.
Mayor Celso Lobregat said the explosions could be connected to an anonymous message sent to his mobile phone, calling for an investigation into an erring government official.
Security forces in the city have been placed on full alert to prevent another attack.