Relations between Egypt's Muslims and Christians degenerated to a new low after riots left 12 people dead and a church burned, adding to the disorder of the country's post-revolution transition to democracy.
The attack on the church was the latest sign of assertiveness by an extreme, ultra-conservative movement of Muslims known as Salafis, whose increasing hostility towards Egypt's Coptic Christians over the past few months has met with little interference from the country's military rulers.
Salafis have been blamed for other recent attacks on Christians and others they do not approve of. In one attack, a Christian man had an ear cut off for renting an apartment to a Muslim woman suspected of involvement in prostitution.
The latest violence, which erupted in fresh clashes between Muslims and Christians who pelted each other with stones in another part of Cairo, also pointed to what many see as reluctance of the armed forces council to act.
The council took temporary control of the country after President Hosni Mubarak was deposed on February 11.
After the overnight clashes in the slum of Imbaba, residents turned their anger towards the military. Some said they and the police did almost nothing to intervene in the five-hour frenzy of violence.
Analysts warned of signs of Coptic violence, especially with reports that some Christians have opened fire at Muslims.
"The Coptic volcano is exploding," Coptic expert Youssef Sedhom said. "How would Copts respond if they find their back to the wall facing guns? They would have no option but self defence. Don't blame Copts for what they do."
Six Muslims were among the dead, according to Egypt's state-run news agency.
Islamic clerics denounced the violence, sounding alarm bells at the escalating tension during the transitional period following Mubarak's February 11 ousting by a popular uprising.