The alleged plot was revealed by the chief of the president's security staff the day before scheduled demonstrations by groups accusing Arroyo of corruption and demanding that she resign, The New York Times reported.

Brig. Gen. Romeo Prestoza, head of the presidential security group, said the plot was developed by the Abu Sayyaf terrorist group and Jemaah Islamiyah, a Southeast Asian extremist Islamic network authorities say operates in the southern Philippines.

"If they want to launch it, they can do it anytime," General Prestoza said.

The alleged plot forced Arroyo to cancel Friday's travel plans to Baguio.

Gen. Hermogenes Esperon, the armed forces chief, confirmed the plot, saying it was the reason why the Philippine military was put on full alert.

The two terrorist groups also were planning to attack "high-value targets" in Manila, Esperon said.

One anti-Arroyo group called the plot disclosure "a desperate scare tactic to discourage people from joining the protests."