Egyptian President Mohammed Mursi faced growing turmoil as clashes between Muslims and Christians led to another death after a religious service held for Copts killed in violence in the previous two days.
The unrest added to the chaos that has convulsed Egypt since Mursi's election in June. Mursi is under assault from an array of critics frustrated that Egypt has seen little of the economic or political revival hoped for after he took office.
Police and armed civilians laid siege to St Mark's Cathedral, the seat of the Coptic church in Cairo, on Sunday, killing one person and injuring at least 23, as a funeral for four Christians killed in sectarian clashes on Saturday descended into chaos.
Thousands of mourners were attacked as they tried to leave, forcing them back inside the cathedral grounds and sparking a siege that stretched into the night. Police fired tear gas over the cathedral walls and stood by as men armed with birdshot, knives and petrol bombs scaled buildings to attack those inside.
On Saturday, at least four Christians and one Muslim were killed in sectarian clashes that broke out in the town of Khosous after children allegedly drew a swastika on Islamic property. It was the deadliest sectarian violence in months, and added a layer of divisiveness at a time of rapidly rising inflation, fuel shortages and deepening poverty.
"Leave!" some protesters chanted in reference to Mursi, echoing the calls that drove his predecessor, Hosni Mubarak, from office during the 2011 uprising. Others, between sobs, yelled: "Down, down, with the Murshid's rule!" a reference to the Muslim Brotherhood's general guide, Mohammed Badie. Others shouted slogans dubbing Mursi a "puppet president". The Muslim Brotherhood fielded Mursi as a candidate for the presidency.
The president's office issued a statement condemning the violence and deploring any attempts to polarise the nation.
Police Major Mohamed Hassan said residents of the district around St Mark's Cathedral hurled rocks and bottles at mourners as they left the service on Sunday.
Ishak Ibrahim, a researcher at the Egyptian Initiative for Personal Rights who monitors religious freedom, said: "Security forces have been very unresponsive since the start of this. We never know who is behind any of the sectarian incidents."
Additional reporting by The Guardian