Egyptian riot police fired tear gas and clashed with dozens of protesters as they tried to tear down a cement wall built to prevent demonstrators from reaching the parliament and the Cabinet building in central Cairo.
The violence came on the eve of the second anniversary of Egypt's uprising which toppled long-time authoritarian President Hosni Mubarak. Three weeks of mass protests that erupted on January 25 2011 eventually forced Mubarak out of office.
Since then, Egypt has undergone a tumultuous transition under the interim leadership of military generals until the election last June of Mohammed Morsi of the Muslim Brotherhood group.
His first six months in office were marked by political tensions, street clashes, and an economic crunch which sapped his popularity.
Thursday's clashes, which left dozens injured, may foreshadow a violent anniversary on Friday when youth activists and opposition groups have called for large rallies in Cairo's Tahrir Square and in front of the presidential palace in the upmarket Heliopolis suburb.
Die-hard fans of Egypt's most popular soccer team, Ahly, took part in the clashes and warned in a statement "The price of blood is blood" in reference to the deaths of many of their friends last year in a violent rampage at a match which left 74 dead.
The group is also calling for mass protests on Saturday, the day a court is expected to rule in a trial of security officials related to the soccer deaths, one of the world's bloodiest instances of violence at a sports event.