PORT-AU-PRINCE, Haiti - December 8, 2010 - The headquarters of Haiti's ruling party was set ablaze Wednesday as riots grew over disputed presidential election results.

Thousands of protesters took to the streets of the capital, erecting barricades and setting fires, furious that government-backed candidate Jude Celestin, the protege of unpopular President Rene Preval, apparently will go on to a runoff vote while carnival singer Michel "Sweet Micky" Martelly finished third in official results and is probably eliminated. Protests have also broken out in Les Cayes, Cap-Haitien and other cities.

Associated Press journalists saw flames leaping from the roof of the Unity party headquarters, the center of Celestin's campaign. Witnesses said the building in central Port-au-Prince was on fire for an hour.

Protesters say security guards shot demonstrators as they assaulted the building, but there were no confirmed injures in the fire or demonstration. Several fire trucks were trying to control the blaze - an unusual scene in a city with few reliable public services.