Al-Sadr said in a statement issued by his office in the city of Najaf that all activities are suspended while the army is being restructured.
In the statement, al-Sadr called on all Al-Mahdi Army offices to cooperate with security forces and exercise "self-control."
Al-Sadr organized the Al-Mahdi Army shortly after the U.S.-led invasion of 2003. Since then it has become a powerful and active armed Shi'ite group, taking part in two uprisings against U.S.-led forces in 2004.
(AFP, AP, BBC)