Manila  - Suspected Muslim separatist rebels bombed a bridge in a southern Philippine city on Monday, but no one was hurt in the attack, a regional military spokesman said.

Major Randolph Cabangbang said the suspects used two homemade bombs in the pre-dawn attack on the Agus bridge in Maria Cristina village in Iligan City, 810 kilometres south of Manila.

"The explosions caused heavy damage on the bridge, adjacent houses and a warehouse of the National Power Corporation," he said. "The bridge at this point is not passable."

Cabangbang said renegade members of the Moro Islamic Liberation Front (MILF) were suspected to be behind the attack, which occurred amid warnings of bombings in the city.

Mayor Lawrence Cruz ordered security forces to step up alert in the city and urged the public to be vigilant against suspicious activities.

He said the Agus bridge, which links the city of the nearby province of Lanao del Norte, would be closed to vehicle traffic until repairs were conducted.

Last year, three people were killed and more than 40 injured when suspected MILF rebels bombed a shopping mall in Iligan City.

The MILF is the largest Muslim rebel group fighting for a separate Islamic state in the southern region of Mindanao. It has been waging the secessionist struggle since 1978. (dpa)