Supporters and opponents of Islamist President Mohamed Morsi have called for protests outside the presidential palace, raising fears of a potential showdown as Egypt’s crisis deepens.

The rallies at the Itihadiya palace — besieged Tuesday by Morsi opponents — are set to square Islamist pro-Morsi demonstrators against his secular-leaning opposition. The two groups until now have only held separate mass protests.

The Muslim Brotherhood called for the rally “to defend legitimacy after (protesters) on Tuesday thought they could impose their opinions through force,” said the movement’s spokesman Mahmud Ghozlan in a statement.

The unrest was sparked by a presidential decree on November 22 granting Morsi sweeping new powers and was exacerbated by a controversial draft constitution, objected to by opponents, which is set for a popular vote on December 15.

Tens of thousands of Egyptians on Tuesday protested against Morsi at the gates of his palace.