Egyptian President's supporters clash with rioters in Cairo

Clashes pitted Egyptian against Egyptian and were the most serious since Morsi's election

A street war was erupting close to the presidential palace in Cairo tonight as the first major clashes broke out between Mohamed Morsi's supporters and opponents outraged over his recent power grab.

In what could herald a dangerous breach within Egyptian society, several thousand protesters hurled rocks and petrol bombs at one and other in the side streets close to the palace.

The east Cairo district of Heliopolis – normally a placid middle-class neighbourhood – was echoing to the sound of exploding fireworks and ambulance sirens tonight.

Smashed masonry and broken glass littered the avenues, while protesters ripped down steel building site barriers to erect makeshift barricades. At one point a fire engine was forced to speedily reverse away from the rioting after being attacked by anti-Morsi protesters.

"There is war in Egypt now," said Ahmad Khatab, a 27-year-old anti-Morsi protester.

Nobel laureate Mohamed el-Baradei, a leading opposition figure and former presidential contender, accused the President's supporters of a "vicious and deliberate" attack against peaceful demonstrators.

"This, in my view, is the end of any legitimacy this regime has," he said. "A regime that is not able to protect its people and is siding with his own thugs is a regime that lost its legitimacy and is leading Egypt into violence."

The battle lines were drawn earlier in the day when thousands of Morsi supporters arrived in Heliopolis to turf out the opposition activists who had conducted a sit-in the previous night.

After being forced away from the palace – the building used by Mohamed Morsi to conduct his official duties – the opposition protesters regrouped and returned en masse a few hours later.

By that time several thousand of the president's supporters – many of them, though by no means all of them, Islamists – had surrounded Mr Morsi's headquarters. When the two groups met, fighting erupted.

In a worrying sign of what could lie ahead, the clashes essentially pitted Egyptian against Egyptian in the most serious disturbances of their kind in the capital since Mr Morsi was elected.

A referendum on Egypt's new constitution is due on 15 December 15. The document has been a bone of contention for Mr Morsi's enemies.