Egyptians gather at Tahrir square in Cairo on the third anniversary of the Arab Spring revolt. 
CAIRO—The third anniversary of Egypt's 2011 uprising was marred by widespread violence on Saturday when at least 29 people were killed and hundreds detained in clashes around the country between police and supporters and opponents of the revolution.
In addition to the 29 dead, at least 176 people were injured, the Health Ministry said. Authorities had deployed security forces in large numbers to try to tamp down violence on the anniversary. More than 400 people were arrested, according to state media.
A series of bomb attacks struck Cairo on Friday, killing and injuring dozens one day ahead of the anniversary of Egypt's revolution against Hosni Mubarak. Via The Foreign Bureau, WSJ's global news update. Photo: AP


Egyptians mark the third anniversary of the Arab Spring
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The driver of a motorcycle and passengers of a bus waved Egyptian flags in the northern port city of Alexandria.
Early Saturday, a small bomb exploded in front of a police training center in the Cairo neighborhood of Ain Shams, according to Egyptian state media. No casualties were reported.
On the eve of the anniversary, 18 people were killed in clashes between police and supporters of Mohammed Morsi, Egypt's first freely elected president, who was ousted in a military coup last year, and a string of bombings in Cairo.
In the weeks leading up to Saturday's commemoration, political parties with widely divergent views sought to lay claim to the day. On Saturday, they took their fight to the streets, sparking clashes between those who support the new military-backed regime and those who see it as a reversal of a once-hopeful revolution.
Several of the deaths occurred in Cairo and neighboring Giza. Tahrir Square was heavily secured but the streets immediately surrounding it were the site of numerous clashes. Other cities also reported widespread violence.
The clashes exposed the deep cracks that remain in society three years after millions united in Cairo's Tahrir Square to demand the ouster of former autocratHosni Mubarak.
Most of the revelers in the square on Saturday were there to celebrate the military-backed government and Gen. Abdel Fattah Al Sisi, the defense minister who ousted Mr. Morsi in July.
In the center of Tahrir Square, a large sign urging Gen. Sisi to run for president was erected. Three years earlier, the demonstrators had hung an iconic banner in the same square, calling for Mr. Mubarak to step down.
Families trickled in wearing Sisi masks and carrying Egyptians flags as nationalist music blared from speakers. The mostly festive atmosphere was punctuated by moments of tension when large groups repeatedly surrounded journalists demanding to know their affiliation.
Two journalists were escorted away under police protection after a mob assaulted them and incorrectly accused them of being employed by Al Jazeera, a television network widely viewed in Egypt as being supportive of the Muslim Brotherhood.
Between chants for Gen. Sisi to run for office, crowds called for the "execution" of the Muslim Brotherhood. Military helicopters flew overhead and periodically dropped small Egyptians flags on the crowd.
A policeman shouts at bystanders to keep away from the site of a blast at the Egyptian security headquarters in downtown Cairo on Friday. 
Some protesters placed police officers on their shoulders and paraded them through the streets, praising them for taking action against the Brotherhood.
"Anyone who is against Sisi is a traitor who wants to bring down Egypt," one man said, declining to be identified. "We've had enough of religious extremism. We're fighting terrorists and who better to do that than a strong man from the military."
The military tightly controlled the entrances to the square with troops, armored vehicles and barbed wire, and patted down demonstrators as they entered.
Saturday also saw limited protests by Mr. Morsi's mostly Islamist supporters. Mr. Morsi was once a leader in the Muslim Brotherhood, an Islamist group whose candidates mostly swept elections following the revolution against Mr. Mubarak in 2011.

An explosion Friday outside the Cairo Security Directorate killed four people. 
But many Egyptians chafed under what they said was Mr. Morsi's overly expansive claims to political authority. Protests erupted when he issued a constitutional declaration in November 2012 that gave him wide authority over judges he considered to be his political enemies.
Since the military ousted Mr. Morsi in early July 2013, Egypt's interim authorities have rounded up tens of thousands of Brotherhood leaders and killed more than a thousand of them while using heavy weapons to subdue almost daily street protests.A third group
of mostly leftist and liberal activists, some of whom refer to themselves as the original revolutionaries or "third way," also organized protests on Saturday.
Immediately outside the square, battles raged between protesters supporting Gen. Sisi and small groups of dissidents demonstrating against both military rule and the Muslim Brotherhood.
The clashes saw all sides hurling rocks, glass bottles and fireworks at each other and ended only when police arrived, dispersing the anti-Sisi crowds with birdshot and tear gas.
Yasser Abdullah, a 23-year-old protester who described himself as an "original Jan. 25 revolutionary" said he opposed both Gen. Sisi and the Muslim Brotherhood.
He had a bloodied lip he said he suffered when a rock struck him in the face.
"Neither way is faithful to our original demands for social justice and democracy," he said. "If I have to get beaten or killed to return to reclaim the revolution, then I am willing to do that today."