Police clashed with protesters in Cairo Thursday, eve of the second anniversary of the uprising that overthrew Hosni Mubarak, as they tried to dismantle a security barrier and called for the fall of Islamist President Mohamed Morsi, an AFP correspondent said.

A few dozens men and youths tried to dismantle the wall of concrete blocks that blocked a street leading to Tahrir Square, focal point of demonstrations that broke out on January 25, 2011 and led to Mubarak's resignation 18 days later.

The walls were erected last year to protect numerous buildings housing government and security service offices in the area.

"Down with Mohamed Morsi," some demonstrators shouted. "Down with the power of the (Supreme) Guide" of the powerful Muslim Brotherhood, from whose ranks Morsi was elected last June.

Some demonstrators hurled rocks at riot police positioned a few dozen metres (yards) on the other side of the wall, who responded with tear gas grenades.

Morsi urged Egyptians on Thursday to mark the revolution's anniversary in a "peaceful and civilised way," in a speech to mark the birthday of the Muslim Prophet Mohammed.

The interior ministry said five policemen were wounded in the clashes and appealed to demonstrators to avoid confrontation with the forces of order and not to attack security barriers set up to protect public and private buildings.

Opposition groups have called for mass street protests across the country on Friday against Morsi and the Brotherhood.

The National Salvation Front, the largest opposition bloc, has called for rallies "in all the Tahrir Squares of the country."

Authorities have vowed to keep security forces out of Tahrir Square to decrease the risk of confrontations, but said police would be in the surrounding areas to arrest troublemakers.