They then raised a flag eerily similar to that used by al-quieda, a black flag of the acclaimed prophet Muhammad. The same thing happened later in the day in Libya. Surprisingly, government police and troops allowed this to happen, no opposition was given to the rioters.
Accordingly , this was in protest to some Christian-Egyptian film producer that lives in the USA. We hear he directed some movie where Muhammad preached violence and had sex with animals.
Regardless of the cause, this is an insensitive act of violence, and a direct result of allowing The Muslim Brotherhood to take over these two countries. Again, look at these examples before you support Syrian Intervention.
Egyptian Muslims attacking an American flag on 9/11