The clashes started after some 4,000 radical Muslim Salafists attacked the St. Mena Coptic Orthodox Church in Cairo's northwestern suburb Imbaba to free a Christian woman they claimed was held against her will because she wanted to convert to Islam.
Later city authorities said the woman had not been held in the church.
CNN quoted Egyptian Interior Ministry spokesman Alla Mahmoud as saying in a statement that 120 were injured in the violence. Al Jazeera's report said 75 received injuries.
The clashes were stopped by police and military.
Egyptian television said unknown assailants set fire to another church in Imbaba after the clashes near the St. Mena Church. The fire was put out.
Egypt's Grand Mufti Ali Gumaa denounced the clashes and called on Egyptians to do everything possible to avoid interfaith confrontation.
Muslims account for some 90% and Christians for about 10% of Egypt's 80-million population.
Relations between the two communities are sometimes darkened by acts of violence, often over Muslims' claims that Christian women who converted to Islam were kidnapped and forcibly held by Copts.
The Christian minority complains of unfair treatment in the country.
MOSCOW, May 8 (RIA Novosti)