At least one person has been killed and 676 people injured in clashes in Cairo after riot police stormed Tahrir Square to clear a protest camp, officials said.
Officers fired rubber bullets, tear gas and beat demonstrators with batons in the Egyptian capital.
Hundreds of protesters fought back, hurling stones and setting an armoured police vehicle ablaze.
The violence spilled into surrounding side streets in downtown Cairo. At least 18 people were reportedly arrested.
The camp had been set up to commemorate hundreds of demonstrators killed in the 18-day uprising that ousted president Hosni Mubarak in February.
The square had been a focal point for the anti-regime protests earlier in the year and activists were trying to restart a long-term sit-in, said witnesses.
"The people want to topple the regime," shouted enraged crowds, reviving the chant from the early days of the uprising.
Crowds also screamed: "Riot police are thugs and thieves" and "Down with the Marshal," referring to Field Marshal Hussein Tantawi, Egypt's military ruler.
The black-clad police were a hated symbol of Mubarak's regime and the latest violence happened just nine days before Egypt's first post-Mubarak parliamentary elections.
On Friday, tens of thousands of Islamists and young activists had massed in the square to protest against Egypt's ruling military council, which took control of the country after Mubarak was deposed.
Public anger is rising at the slow pace of reforms and apparent attempts by Egypt's ruling generals to retain power over a future civilian government.