At least 24 people have died in the Egyptian capital, Cairo, after Sunday’s clashes between military police and mostly Coptic Christian demonstrators.
Medics said more than 200 people were injured in the violence.
The Copts said they were subjected to an unprovoked attack after what they called a peaceful protest against the destruction of a church in southern Egypt.
Security sources said the protesters torched vehicles and threw rocks, forcing officers to move in.
Egyptian Prime Minister Essam Sharaf called for calm, stressing that discord between Muslims and Christians in Egypt would be “a threat to the country’s security”.
“From here I call on every Egyptian not to listen to rumours and not to act upon slander, for the state is in danger as a result of these consecutive events which reflect obvious harm to the nation’s capabilities”, Sharaf said in a speech on state television.
The clashes amount to some of the worst violence since a February uprising ousted former leader Hosni Mubarak.
The Copts make up some ten percent of Egypt’s 80 million-strong population.
They accuse the country’s interim military rulers of being too lenient on those who carry out sectarian attacks on Christians.