Clashes between protesters and Egyptian security forces have intensified at the site of a bloody confrontation a year ago in Cairo, when 42 people were killed in a street battle months after the uprising that ousted the country's long-time president.
Hundreds of demonstrators threw rocks at police, who fired tear gas and fired birdshot in response.
A medical official said 60 protesters and 10 policemen were injured.
The clash was a small scale reprise of one of the fiercest confrontations after last year's popular revolution, when the protesters who brought about the overthrow of long-time President Hosni Mubarak returned to the streets to demonstrate against the harsh measures imposed by the military, which took over from the ousted leader.
The persistent unrest reflects divisions plaguing Egypt 21 months after Mubarak's downfall in February 2011.
While young, mostly secular activists spearheaded the uprising, the main winners in the aftermath have been fundamentalist Islamic movements - the Muslim Brotherhood, which won elections for parliament and president, and the more extreme Salafis, who have also shown considerable electoral strength.
That has left the frustrated liberal activists on the outside, demonstrating against both the military and the Brotherhood.
Yesterday protesters tore down a cement block wall between Cairo's downtown Tahrir Square, the focus of huge demonstrations last year, and the headquarters of the security forces.
While the casualties were lower, many of the scenes were almost eerily the same as a year ago.
Protesters riding motorbikes rushed the injured to a field hospital. Others carried pictures of demonstrators killed in last year's crackdowns by the military.
Demonstrators hung a banner read, "Muslim Brotherhood not allowed," while others chanted, "the people want to topple the regime," referring to Islamist President Mohammed Morsi, whose Muslim Brotherhood avoided street confrontations with the military rulers last year to focus instead on campaigning and elections.
Protester Abdullah Waleed said the protest was aimed at opening main roads that have been blocked for a year.
"While we were tearing down the cement blocks, security forces fired at us," he said. "I was wounded by (shotgun) pellets."
Last year's street battle, known as "Mohammed Mahmoud" after the name of the street where it unfolded, was triggered by a security crackdown on a sit-in by injured protesters.
It set off days of sustained violence, with security forces firing tear gas, shotgun rounds and rubber bullets, wounding hundreds.
The street became a symbol of the uprising and an open-air museum. Walls were filled with graffiti, slogans and images of the revolution.
For 17 months after Mubarak's ouster, the Supreme Council of the Armed Forces (SCAF) ruled Egypt in a turbulent transition period that saw a surge in crime, deterioration of economy and frequent deadly street clashes.
The council, led by Field Marshal Hussein Tantawi, was eased out of power after the election of Morsi in the country's first free elections in decades.
Morsi took office at the end of June.
The tensions have not disappeared, as evidenced by Monday's bitter confrontations.
Even members in different security forces battled each other.
An Egyptian security official said clashes erupted between civilian police and military forces in northern Cairo after police arrested a military officer over a traffic violation.
Hundreds of soldiers encircled the police station where the officer was being held, trying to storm the station, while the police fired tear gas to disperse them, the official said.
The incident reflected a feeling among many that the military is acting as a state within a state. The official spoke on condition of anonymity because he was not authorized to speak to reporters.
The violence comes during tensions over the writing of Egypt's new constitution.
Members of several liberal parties and representatives of Egypt's churches have announced their withdrawal from the 100-member constituent assembly tasked with writing the document, protesting what they perceive as attempt to impose ultraconservative Islamist content.
Liberals fear that would be the first step toward strict implementation of Islamic Shariah laws, endangering civil liberties, as well as the rights of minorities and women.