CAIRO (AP) — Thousands of Egyptians demanding the ouster of Egypt's Islamist president are gathering at Cairo's central Tahrir Square at the start of a day of massive, nationwide protests many fear could turn deadly.

Sunday marks the first anniversary of President's Mohammed Morsi's assumption of power as Egypt's first freely elected leader.

Thousands of Morsi's supporters have staged a sit-in since Friday in an eastern Cairo district not far from the presidential palace, the focus of protests later on Sunday to demand his ouster.

The youth group leading the campaign to force Morsi out said it had collected more than 22 million signatures from Egyptians who want the president to go. It was not possible to verify the claim.

Morsi's supporters have questioned the authenticity and validity of the signatures.