CAIRO – Egypt descended into political turmoil on Wednesday, violence flaring up over the constitution drafted by Islamist allies of President Mohammed Morsi. At least 211 people were wounded as supporters and opponents battled each other with firebombs, rocks and sticks outside the presidential palace.

Four more presidential aides resigned in protest over Morsi’s handling of the crisis, and a key opponent of the Islamist president likened Morsi’s rule to that of ousted authoritarian leader Hosni Mubarak.

Both sides were digging in for a long struggle, with the opposition vowing more protests and rejecting any dialogue unless the charter is rescinded, and Morsi pressing relentlessly forward with plans for a Dec. 15 constitutional referendum.

“The solution is to go to the ballot box,” declared Mahmoud Ghozlan, a spokesman for Morsi’s Muslim Brotherhood, asserting the charter was “the best constitution Egypt ever had.”

The clashes outside the presidential palace in Cairo’s Heliopolis district marked an escalation in the deepening crisis. It was the first time supporters of rival camps have fought each other since last year’s anti-Mubarak uprising, when the authoritarian leader’s loyalists sent sword-wielding supporters on horses and camels into Cairo’s Tahrir square in what became one of the uprising’s bloodiest days.

The large scale and intensity of the fighting marked a milestone in Egypt’s rapidly entrenched schism, pitting Morsi’s Brotherhood and ultra-conservative Islamists in one camp, against liberals, leftists and Christians in the other.