BBC News reports:
Mourners leaving St Mark's Cathedral clashed with local residents.
Police fired tear gas to break up the violence. More than 80 people were injured, the state news agency said.
The health ministry said one Christian man was killed. The ambulance service said he was struck with birdshot.
Mourners inside the church had earlier chanted slogans against Egypt's Islamist President, Mohammed Morsi.
Witnesses told local TV stations that the violence started when a mob attacked mourners as they exited the cathedral, pelting them with stones and petrol bombs. There was initially little police presence.
The Christians responded by throwing stones back, the witnesses said, until police arrived and attempted to quell the unrest, firing tear gas into the cathedral compound.