Egyptian protesters have clashed with riot police in Cairo's Tahrir Square, where thousands of demonstrators have gathered to mark the second anniversary of the uprising that brought down longtime leader Hosni Mubarak.
The skirmishes began early Friday after youth protestors tried to approach a concrete wall that security forces had erected to secure government buildings in the area.
Demonstrators threw incendiary devices and rocks at police, who responded by firing tear gas and setting some of the protesters' tents in the square on fire.