Police have clashed with protesters gathering in Tahrir Square in the Egyptian capital, Cairo, ahead of the second anniversary of the uprising that swept Hosni Mubarak from power.
President Mohammed Morsi’s opponents plan a rally, accusing the Islamist leader of betraying the revolution – a claim Mr Morsi denies.
Instead, he urged the nation to mark the revolution in a “peaceful way”.
Mubarak, 84, was jailed for life over the deaths of some 850 protesters.
On Thursday evening, police clashed with protesters who tried to remove barriers blocking a road to Tahrir Square.
Mr Morsi’s Muslim Brotherhood party has not officially called for its own street rallies. It plans to mark the revolution by launching charitable and social initiatives.
Earlier this month a court ordered a retrial for former President Mubarak.
The opposition says it expects large crowds to gather in the Tahrir Square later on Friday.
It accuses Mr Morsi of being autocratic and driving through a new constitution that favours Islamists and does not sufficiently protect the rights of women or Christians.
The new government is also being blamed for a deepening economic crisis.
Mohamed ElBaradei, a leading opposition figure and former head of the UN atomic agency, wrote on Twitter ahead of the planned rally: “Go out into the squares to finally achieve the objectives of the revolution.”
Similar protests are expected in other Egyptian cities.
President Morsi and his party reject the opposition’s accusations as unfair, instead calling for a national dialogue.
Last month, Mr Morsi described the new constitution as historic and also said that boosting Egypt’s economy was his priority.
He also admitted that mistakes had been made but insisted he would never make a decision except in the interests of the country.