The headquarters of Egypt's liberal Wafd Party in Cairo was torched on Saturday by supporters of Salafi Islamist politician Hazem Salah Abu Ismail, an Al Arabiya correspondent reported.
Four people, including one policeman, were injured in the attack, in which the radical Islamist's supporters managed to break into the party's building despite heavy security presence, The Voice of Russia reported.
The violence broke out as Egyptians voted in a referendum on a new constitution intended to pull the country out a growing political crisis.
The first round of voting was held in ten provinces, icluding the capital Cairo and Alexandria.