BAGHDAD (AP) — Riot police used water cannons to repel demonstrators pulling down cement blast walls Wednesday at Baghdad's heavily fortified Green Zone, home to government buildings and foreign embassies.

The standoff marks the biggest protest since federal elections were held in October.

The demonstrators gathered to protest the recent nomination for prime minister by Iran-backed political groups. They chanted against the selection of Mohammed al-Sudani as the official nominee of the Coordination Framework bloc, a coalition led by Iran-backed Shiite parties and their allies.

Riot police forces assembled at the doors to the main gates. Demonstrators crowded around two entrances to the Green Zone, with some scaling the cement wall and chanting, “Sudani, out!"

The demonstrators were largely followers of influential Shiite cleric Muqtada al-Sadr, who recently stepped down from the political process despite having won the most seats in the October federal election. Protesters carried portraits of the cleric.

Al-Sudani was selected by State of Law leader and former premier Nouri al-Maliki. Before al-Sudani can face parliament to be seated officially as premier-designate, parties must first select a president.

Al-Sadr exited government formation talks after he was not able to corral enough lawmakers to get the majority required to elect Iraq’s next president.

By replacing his lawmakers, the Framework leader pushed ahead to form next government. Many fear doing so also opens the doors to street protests organized by al-Sadr's large grass roots following and instability.