A bomb exploded outside a shop in southern Philippine island of Mindanao Wednesday causing damage but no injuries a day after two blasts killed at least six people, police said.

The explosion occurred at 12:10 p.m. in front of the South Sea Mall in Cotabato City, said Chief Superintendent German Doria, Central Mindanao police director.

The bomb blast came hours after the Philippine National Police announced that it had raised the alert levels in Metro Manila and Mindanao because of the attacks.

Hours before the latest explosion, authorities in Makilala town in North Cotabato discovered a fourth bomb near the municipal hall. Authorities were able to prevent the bomb from exploding.

In Manila, Armed Forces chief Hermogenes Esperon said that he believes that the bomb attacks were carried out by the Abu Sayyaf and the Jemaah Islamiyah in retaliation for the arrest of an international terrorist's wife.

Esperon was quoted by GMA TV as saying that they began receiving reports about bombing attacks after the arrest of Istiada Sovie Oemar, the wife of Indonesian terrorist Dulmatin, and their two sons in Sulu.

The Armed Forces chief added that the bombings could also be part of an attempt by the terrorist to divert the attention of the military from it ongoing offensive in Jolo.

Two explosions hit the major southern island of Mindanao on Tuesday, killing six people and injuring over 30 others in separate incidents.

The United States and Australia issued travel advisories against the Philippines on the same day when the explosions occurred.

In a statement posted on its website, the U.S. Embassy in Manila said it received "credible information" of an imminent attack in central Mindanao "over the next several days."

Source: Xinhua