There were massive riots in Cairo last night with at least 24 dead and hundreds injured. The rioters were Coptic Christians fed up with Muslims attacking their churches and the authorities standing by and doing nothing.
Egypt's cabinet is set for an emergency meeting and the first funerals of the 24 people who died are to be held.
Riots erupted on Sunday after a protest against an attack on an Aswan church.
Reports of protesters in Cairo being crushed by military vehicles have heightened tensions further.
Sectarian strife has increased in recent months in Egypt.
The Copts - who make up about 10% of the population - accuse the governing military council of being too lenient on the perpetrators of a string of anti-Christian attacks.
The BBC's Yolande Knell in Cairo says there is pressure on ministers and on the country's military rulers to give assurances about national unity.
One can imagine the plight of Christians in Egypt once the Muslim Brotherhood is in charge.
The violence began outside the state TV building but soon spread to Tahrir Square, the epicentre of the demonstrations which led to President Hosni Mubarak's resignation February.
There were reports of thousands joining in the street violence, attacking both sides. Rioters tore up the pavement and hurled stones.
Correspondents say that many Muslims came out to defend Christians from the security forces and protest against the military's continued hold on power.
Some called for the resignation of the military council, in particular its chairman, Field Marshal Mohamed Tantawi.
Others responded to government calls to help the army quell the unrest for the sake of stability.
Some protesters reported hearing gunfire, and several said they had seen a military vehicle run over at least five people. There has been no comment from the government on the reports.
How many Muslims came out to attack the protesters versus how many came out to defend them? The authorities encourage the former, of course, and they are driving the Christians into extremism to defend their faith and their lives.
This will not be the last riot in Cairo nor will it be the end of Christians killed. Egypt is broken and, like millions of other Christians in the Middle East, Egypts ancient Coptics are finding Islamic extremists would rather kill them than live with them.