26 January 2013
Last updated at 00:54
Egyptian opposition supporters marked the second anniversary of the uprising that ousted President Hosni Mubarak with a mass rally in Cairo's Tahrir Square. Some chanted slogans used during the 2011 uprising, including: "The people want the overthrow of the regime."
Two years on, Egypt is deeply divided between Islamists, who insist they won a clear mandate in recent elections, and liberals, secularists and Christians.
Some protesters threw stones, while others tried to pull away razor wire protecting Cairo's presidential palace.
Police responded by firing tear gas.
Protesters say President Mohammed Morsi and the Muslim Brotherhood, the Islamist movement to which he belongs, are betraying the promises of the revolution.
The protests are seen as a show of force aimed at forcing Mr Morsi to amend the constitution drafted by his Islamist allies and passed in a referendum last month. Critics say it fails to protect freedom of expression and religion.
Clashes also erupted during similar protests in several other cities, including Alexandria, where at least 18 protesters were reportedly injured.
Leaders of the secular opposition - including Hamdeen Sabahi and Mohamed ElBaradei - appeared in Cairo's Tahrir Square to mobilise supporters
Protesters blocked one of Cairo's busiest bridges and also Anwar Sadat metro station at Tahrir Square.
Thousands of people joined the demonstrators following Friday prayers - which many attended in Tahrir Square itself.
The Muslim Brotherhood and its ultraconservative Salafist allies have said they will not hold rallies on the anniversary of the revolution.