Egyptian security forces have fired tear gas and protesters hurled stones and Molotov cocktails in a day-long demonstration, raising fears of a violent anniversary of the 2011 uprising that toppled President Hosni Mubarak.
Youth activists and opposition groups have called for large rallies on the anniversary on Friday in Cairo's Tahrir Square and in front of the president palace in the Heliopolis suburb.
Thursday's clashes, which left dozens injured, began after protesters in central Cairo tried to tear down a cement wall built to prevent them from reaching the parliament and the Cabinet building.
"Down with Mohamed Morsi," some demonstrators shouted in reference to the president. "Down with the power of the [Supreme] Guide" of the Muslim Brotherhood, from whose ranks Morsi was elected last June.
The street clashes continued into the late evening.
Since three weeks of mass protests forced Mubarak out of office, Egypt has undergone a tumultuous transition under the interim leadership of military generals until the election of Morsi.
His first six months in office were marked by political tensions, street protests and an economic crunch that lowered his popularity.
Morsi visited the western city of Ismailia on Thursday to inaugurate a maritime project, but was received by activists who blocked a railway station, tore down the welcoming banners and issued a statement stating that they were opposed to inaugurating new projects while there is corruption in the railway system.
Later in the day, the president urged Egyptians to mark the anniversary peacefully.
"I call upon Egyptians to celebrate the revolution ... with civilisation and peacefully to preserve our nation, our institution, our souls, our streets and our sons," he told a gathering in a speech meant to mark the birthday of Muslim Prophet Muhammad.
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"We have to feel that we are all in one ship and we have to preserve its safety and respect the people and their free will which they express in their ballot boxes."
The National Salvation Front, the largest opposition bloc, has called for rallies across the country on Friday, "in all the Tahrir Squares of the country".
Authorities have vowed to keep security forces out of Cairo's Tahrir Square to decrease the risk of confrontations, but said police would be in the surrounding areas to arrest troublemakers.
Fans of Egypt's most popular soccer team, al-Ahly, who took part in Thursday's clashes, warned in a statement: "The price of blood is blood". It was a reference to the deaths of many of their friends last year in a violent rampage at a football game that left 74 people dead.
The soccer fans, known as Ultras, also called for mass protests on January 26, the day a court is expected to rule on the fate of security officials being tried in connection with the deaths at the game, one of the world's bloodiest instances of violence at a sports event.
In addition to Ultras, a previously unknown group calling itself the Black Bloc appeared in a video clip posted on social networking sites. Wearing black masks and waving black banners, it warned the Muslim Brotherhood of using its "military wing" to tamp down protests, saying that if it did it would "go down to the streets and never come back".
In another online statement, the Black Bloc claimed responsibility for attacks on the offices of the Muslim Brotherhood and a fast-food chain known to be owned by the group.