Egyptian security forces fired tear gas and protesters hurled stones and Molotov cocktails in a day-long demonstration on Thursday, raising fears of a violent anniversary of the 2011 uprising that toppled long-time authoritarian President Hosni Mubarak.
Youth activists and opposition groups have called for large rallies on the anniversary Friday in Cairo's Tahrir Square and in front of the president palace in the upscale suburb, Heliopolis.
The protests, which left dozens injured, began before dawn in central Cairo when protesters tried to tear down a cement wall built to prevent them from reaching the parliament and the Cabinet building. The street clashes continued after darkness fell on the Egyptian capital.
Three weeks of mass protests that erupted on Jan. 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 protests and an economic crunch that sapped his popularity.
As the protests continued, Morsi visited the western city of Ismailia to inaugurate a maritime project, but he 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's corruption in the railway system.
Later in the day, Morsi urged Egyptians to mark the anniversary peacefully.
"I call upon Egyptians to celebrate the revolution ... with civilization 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.
"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," he added.
But die-hard fans of Egypt's most popular soccer team, Ahly, who took part in the 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 soccer game that left 74 dead.
The soccer fans, known as Ultras, also called for mass protests on Jan. 26, the day a court is expected to rule on the fate of security officials being tried in connection with the deaths at the soccer game, one of the world's bloodiest instances of violence at a sports event.
On Tuesday, in an attempt to assuage anger, Morsi announced that the victims will be considered "martyrs." That means their families will receive compensation like those killed in the uprising against Mubarak.
That same day, Egypt's prosecutor general, who was appointed by Morsi, asked the court to give the prosecution more time to introduce new findings and new defendants before issuing its verdict. That was seen viewed as a move to postpone the verdict and avoid street violence by the soccer fans.
On Wednesday, Ultras held a sit-in in front of Egypt's stock market, briefly blocked a highway, and set up tents in Tahrir Square. The group has long been at odds with police, and it played a key role in anti-Mubarak uprising.
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. Egyptian daily Al-Masry al-Youm reported that members of the group took part in Thursday's clashes.
The opposition has demanded a suspension or radical changes to be made to Egypt's newly adopted constitution, which an Islamist-dominated constituent assembly drafted amid deep polarization and mass street protests.
The constitution, which many Egyptians see as a detrimental to civil liberties and a precursor to a religious state, passed with a 64 percent "yes" vote in a December referendum in which around 33 percent of voters took part.
In an online video message posted on Thursday, the nation's most prominent opposition leader Mohamed ElBaradei urged Egyptians to rally in the streets but warned that change will take time.
"I demand from each one of you, all across Egypt, to prove that the revolution must continue and must be completed," ElBaradei, a Nobel Peace Prize laureate and former head of the U.N. nuclear agency, said in the message.
"Egyptians rose up for the sake of freedom, dignity and social justice," he said. "We must not stop until we see all the demands achieved. It will take time but we have to put ourselves on the right path."
The opposition wants to use the occasion to put pressure on Morsi and the Muslim Brotherhood, who secular and liberal Egyptians accuse of trying to monopolize power.
Meanwhile, the Brotherhood and other Islamist parties announced they will stay away from the streets on Friday's anniversary and warned the opposition against instigating violence. However, a Brotherhood member said that orders were given for supporters to rally at a mosque located near the presidency. He spoke on condition of anonymity because he was not authorized to give the information to the media.
Egypt witnessed some of its worst street clashes on Dec. 4 when supporters of the Muslim Brotherhood clamped down on tents and protesters holding a sit-in in front of the presidential palace. Clashes ended with 10 dead and hundreds injured on both sides.
The Brotherhood said it would mark the anniversary by planting 1 million trees in a campaign entitled "Let's build Egypt."
In a statement posted on the group's official website, its leader, Mohammed Badie, advised Muslims to "watch their enemies," invoking challenges the prophet faced while founding a new state in the holy city of Medina in the 7th Century.
Commemorating the prophet's birthday, a national holiday, Badie said Muhammad faced "hypocrites, filled with hatred and envy for the emerging group."