Background via the Wall Street Journal:

Clashes between Muslims and Christians in downtown Cairo on Sunday night left at least 24 people dead, including three Egyptian military police officers, in one of the worst incidents of sectarian violence since a revolution in February toppled Egypt’s former regime…

“People are burning churches!” said Nasser Abdel Mohsen, a Muslim who said he had joined the Christian protesters out of solidarity. “That’s never happened before. We always used to live peacefully as Copts and Muslims.”…

In the most recent church attack late last month, a mob led by fundamentalist Muslims burned and defaced a church near the city of Aswan. Gangs of local Muslims had objected to renovations to the church, which they said was built without a permit.

The attacks occurred even after church officials had acquiesced to demands from local Salafis to remove bells and crosses from the church’s facade.