In Manila, riot police have clashed with supporters of presidential candidate Fernando Poe Jr. - ahead of a Supreme Court decision on whether the popular action movie star should be disqualified from May elections.

In tense scenes in Manila, riot police used water cannons and batons to disperse several hundred supporters of presidential hopeful Fernando Poe, who planned to march on the Supreme Court Thursday.

Thousands of police have been mobilized to protect the court, which has been hearing oral arguments over whether Mr. Poe - born to a Filipino father and an American mother - is a "natural born Filipino citizen." If it finds he is not, under the constitution, Mr. Poe would be barred from standing in the May election.

Public opinion surveys show Mr. Poe is the frontrunner. His supporters have accused his opponents of unfairly trying to have him barred from the election race.

Opinion is divided over the case. But local political analyst, Ronald Llamas, believes constitutional law experts could sway the court in Mr. Poe's favor. "I think based on their initial positions on the issue, it will be very liberal and to a great extent they would suggest that the Supreme Court directly or indirectly don't disqualify Fernando Poe Jr.," says Mr. Llamas.

The government of President Gloria Arroyo has also ordered a thousand soldiers on standby when the ruling is issued - possibly sometime this week. The government fears a repeat of riots that rocked Manila in 2001 when former President Joseph Estrada - a close friend of Mr. Poe - was forced from office in a popular uprising. Ms. Arroyo, backed by the military, assumed the presidency in what the court has ruled was a legal succession of power.