Christian leaders in Egypt appealed for calm after a mob attacked St. Mark's Coptic Orthodox Cathedral in Cairo on Sunday during the funeral of four Coptic Christians killed in sectarian clashes.

At least two Christians died and over 80 were injured in the Sunday attacks, which marked the third day of sectarian violence, according to the Christian Post.

Pope Tawadros II, the Patriarch of the Coptic Orthodox Church said the Egypt must "keep calm" to preserve security and national unity.

The Council of Churches in Egypt condemned the attack and called for "immediate action" from the government, Fides news agency reports.

Egyptian president Mohammed Morsi told Patriarch Tawadros by phone that he is committed to stopping the violence and that he considers "any attack against churches as a personal attack" against him.

On Friday a dispute in the town of Khusus near Cairo turned into a gunfight that killed four Christians and a Muslim.

After the Christians' funeral Sunday, Christians left the cathedral and joined sympathetic Muslims to chanting slogans against President Mohammed Morsi. They called for his removal and the removal of his allies.

Violence broke out, though it is unclear how it started. Assailants were few at first, but their numbers grew to over 200 people.

They stationed themselves on the roofs of buildings surrounding the cathedral, attacking Christians and others with stones and petrol bombs until late in the evening, Fides News Agency reports.

Security forces and riot police appeared to have sided with the Muslim men who were attacking the Christians, the New York Times says.

Christians took up the defense of the cathedral and threw fire bombs and brick shards at the riot police, some of whom were injured.

Egypt's Interior Ministry has charged that the mourners had started the attacks by vandalizing cars, which led to clashes and fights with others in the area.

Coptic Christians, who are descendants of Egypt's pre-Muslim population, make up about 10 percent of the predominantly Muslim population of Egypt.