There are conflicting reports on how exactly the clashes erupted.
Some of them write that mourners who were chanting against the ruling Muslim Brotherhood were pelted with stones as they left the church.
Egypt Independent writes that the violence broke out after unknown assailants attacked people attending the church service held at St. Mark’s Coptic Orthodox Cathedral in the Abbasseya neighborhood in the Egyptian capital.
One person was reported dead at the nearby Demerdash hospital, citing the head of the ambulance services.
The victim was killed after having been struck by birdshot outside the cathedral, said the head of the Egyptian Ambulance Organization, Mohamed Sultan.
The Health Ministry confirmed at least 66 wounded in the clashes, Egypt Independent wrote. Two of the injured are said to be in a critical condition.
Riot police used tear gas to disperse the crowd.
Egyptian President Mohamed Morsi has slammed the violence telling Coptic Pope Tawadros II "Any attack against the cathedral is like an attack on me personally", state news agency MENA reports.
Meanwhile, "Men continue to flood the Cathedral, some holding sticks, rocks," Egypt Independent reports on Twitter. "Outside people chant against the regime amid periodic loud booming sounds."
Pope Tawadros II has issued an official statement urging the Egyptian people to exercise "wisdom and restraint."
Confrontations between Christians and Muslims have increased in the Muslim-majority Egypt after the overthrow of President Hosni Mubarak in 2011.
On Saturday, sectarian violence left four Coptic Christians and one Muslim dead in al-Khusus, northeast of Cairo.
