The legitimacy of Egyptian President Mohamed Morsi is hanging by a thread, leading opposition figure Mohamed ElBaradei said following Wednesday’s clashes that erupted in front of the presidential palace in Cairo.

An afternoon attack by Morsi supporters against anti-Morsi protesters, who began a sit-in in front of the palace on Tuesday, has sparked clashes that left dozens injured so far.

“Morsi bears full responsibility for what is happening. If he doesn’t intervene to stop the bloodshed, we will turn to the legitimacy of the revolution, not the constitution,” ElBaradei told a news conference.

ElBaradei was flanked by former presidential candidates Hamdeen Sabbahi and Amr Moussa, both of whom have joined the reform campaigner in establishing a “National Salvation Front” to oppose Morsi’s controversial decree.

Morsi opponents demand that he cancels a recent decree, which shields his decision from judicial review, and call off a scheduled referendum on a newly-draft constitution, which is slated for 15 December. Protesters say the constitution only represents Islamists, disregarding the rights of liberals, women, workers, and Christians.

The president’s supporters believe the decree is necessary to tackle what they describe as judicial corruption. They also support a “yes” vote in the constitution referendum, which will pave the way for new parliament elections.

“The Brotherhood are the ones who disregarded laws and constitution. We will not sit down with Morsi unless he cancels the decree nor we will make any initiatives. He is the one should make an initiative,” ElBaradei added.

“We will use all peaceful means to bring down the constitutional declaration, including civil disobedience.”