BAGHDAD - Four rockets were fired on the heavily fortified Green Zone overnight and in the morning after Shiite cleric Moqtada al-Sadr resigned from politics, sparking protests by his supporters in which up to 22 people were killed and more than 200 were injured, according to the Iraqi military on Tuesday.

According to a statement from the Iraqi Joint Operations Command's media office, the rockets were launched from Baghdad's eastern neighborhoods of al-Habibiyah and al-Baladiyat and landed on a residential compound inside the Green Zone, which houses some of the main government buildings, residences of Iraqi top officials, and some foreign embassies.

The rockets caused no human casualties except for some damages, the statement said.

Meanwhile, overnight clashes between Saraya al-Salam, or Peace Companies, loyal to al-Sadr, and militiamen believed to be affiliated with al-Sadr's opponent from the other Shiite parties occurred in the Green Zone and other areas of Baghdad.

The clashes resulted in the killing of 22 people and the wounding of more than 200 others, the Baghdad Operations Command said in a statement.

Late Monday night, an Interior Ministry source told Xinhua anonymously that at least 12 protesters and security personnel were killed and dozens were injured, primarily as a result of tear gas canisters and sporadic shootouts from unknown gunmen against the protesters inside the zone.

On Monday, tensions were further escalated after al-Sadr's supporters stormed some of the main government headquarters in the Green Zone following their leader's announcement that he was quitting politics in protest against the corruption of political parties in the country.

Local media footage showed dozens of protesters inside the presidential palace at the edge of the Green Zone, which was evacuated before protesters stormed it.

Al-Sadr supporters also took to the streets in several provinces south of Baghdad, including Basra, Maysan, Dhi Qar, and Wasit, according to local media.

Political disputes have escalated in the past weeks between al-Sadr and his rivals in the Coordination Framework (CF), an umbrella group of Shiite parliamentary parties.

On July 30, al-Sadr's followers broke into the Green Zone and held an open sit-in in and outside the parliament building, demanding the dissolution of the parliament and early elections, all of which were rejected by the CF parties.

During the past months, the continued disputes among the Shiite parties have hampered the formation of a new Iraqi government, making it unable to elect a new president by a two-thirds majority of the 329-seat parliament under the constitution.

If elected, the president will appoint the prime minister nominated by the largest alliance in the parliament, now the CF, to form a new government that would rule the country for the next four years.