Flames lit up downtown Cairo Sunday night, following a day of massive clashes that pitted Coptic Christians angry over a recent church attack against Muslims and Egyptian security forces.

At least 24 people have been confirmed dead and more than 200 injured in the worst sectarian violence since the uprising that ousted Hosni Mubarak in February

The clashes lasted late into the night, bringing out a deployment of more than 1,000 security forces and armoured vehicles to defend the state television building, where the trouble began. The clashes spread to nearby Tahrir Square, drawing thousands of people to the vast plaza that served as the epicentre of the protests that ousted Mubarak.

Demonstrators and security officers battled each other with rocks and firebombs, some tearing up pavement for ammunition and others collecting stones in boxes.

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An injured Egyptian Coptic demonstrator is taken away by fellow protesters. (Nasser Nasser/Associated Press)

Hundreds of Christian protesters chanting "This is our country" burned vehicles. Christians blame Egypt's ruling military council for being too lenient on those behind a spate of anti-Christian attacks since the ouster of Mubarak.

Prime Minister Essam Sharaf, addressing the nation in a televised speech, said the violence threatened to throw Egypt's post-Mubarak transition off course.

"These events have taken us back several steps," he said. "Instead of moving forward to build a modern state on democratic principles we are back to seeking stability and searching for hidden hands -- domestic and foreign -- that meddle with the country's security and safety."

"I call on Egyptian people — Muslims and Christians, women and children, young men and elders — to hold their unity," Sharaf said.

Witnesses said some of the protesters may have snatched weapons from the soldiers and turned them on the military. The protesters also pelted the soldiers with rocks and bottles. The clashes spread to nearby Tahrir Square and the area around it, drawing in thousands of people.

At one point, an armoured security van sped into the crowd, striking a half-dozen protesters and throwing some into the air. Protesters retaliated by setting fire to military vehicles, a bus and private cars, sending flames rising into the night sky.

After midnight, mobs roamed downtown streets, attacking cars they suspected had Christian passengers. In many areas, there was no visible police or army presence to confront or stop them.

"The protest was peaceful. We wanted to hold a sit-in, as usual," said Essam Khalili, a protester wearing a white shirt with a cross drawn on it. "Thugs attacked us and a military vehicle jumped over a sidewalk and ran over at least 10 people. I saw them."

Khalili said protesters set fire to army vehicles when they saw them hitting the protesters.

Thugs chase protesters

Thugs with sticks chased the Christian protesters from the site, banking metal street signs to scare them off. One soldier collapsed in tears as ambulances rushed to the scene to take away the injured.

Television footage of the riots showed some of the Coptic protesters attacking a soldier, while a priest tried to protect him.

The rally began in the Shubra district of northern Cairo, then headed to the state television building overlooking the Nile where men in plainclothes attacked the Christian protesters. It was not immediately clear who the attackers were.

Egypt's Coptic Christian minority makes up about 10 per cent of the country's population of more than 80 million people. As Egypt undergoes a chaotic power transition and security vacuum in the wake of this year's uprising, Christians are particularly worried about the increasing show of power by the ultraconservative Islamists.

"Our protest is peaceful and I don't know why they attack us," said Rami Kamel, a Coptic protest leader.

In the past weeks, riots have broken out at two churches in southern Egypt, prompted by Muslim crowds angry over church construction.