During Post-invasion Iraq, Operation Iron Saber was a coalition strike aimed at defeating the Mahdi Army under the control of Muqtada al-Sadr in Najaf, Diwaniyah, Al Kut and Karbala. The major American unit involved was the 37th Armor Regiment of 1st Armored Division. The operation was launched in April 2004, and after intense urban warfare which involved Mahdi militiamen taking refuge in mosques, coalition forces had defeated the Mahdi army by June and had forced a cease-fire with al-Sadr.