"We declare the freezing of the Mahdi Army without exception in order to rehabilitate it in a way that will safeguard its ideological image within a maximum period of six months," al-Sadr aide Sheik Hazim al-Araji announced Wednesday, reported the Associated Press.
The recent violence in Karbala began with the mass pilgrimage of Shiites to the holy city for a festival held earlier this week.
"The fighting forced authorities to cut short the annual Shabaniya festival, which drew an estimated 1 million people from across the Shiite world," reported the AP.
Violence was initiated when police clashed with pilgrims who were trying to get through security checkpoints hear the Imam al-Hussein mosque, one of the main sites of the celebration. Five were killed.
As clashes escalated, "gunmen believed from the Mahdi Army began firing on security forces and the Badr guards, according to security officials," the AP reported.
Battles between the Badr Organization, the armed wing of the Supreme Islamic Council of Iraq and al-Sadr's Mahdi Army rose with the firebombing of Iraqi Prime Minister Nouri al-Maliki's Karbala office and battles near two Shiite shrines. The violence left at least 52 dead and injured hundreds.
The aide to al-Sadr "announced three days of mourning and the closing of al-Sadr's offices for the same period of time to condemn the events in Karbala," CNN reported.
Al-Sadr, a grassroots Shiite cleric, first gained popularity just after the fall of Saddam Hussein in 2003. The staunchly anti-U.S. leader has blamed the United States for driving thousands of Sunnis from their homes in retaliation for Sunni extremist attacks on Shiite civilians, according to the AP.
Despite al-Sadr's past involvement in attacks on U.S. forces in Karbala and Baghdad, the United States supported the cleric's move to suspend the army.
"We have always said we welcome those who want to participate positively in the future of Iraq," said Lt. Col. Christopher Garver, a U.S. military spokesman, according to CNN. "U.S. forces welcome anyone and any leader who attempts to bring down the violence and rein in criminal behavior."