The demonstration was called by supporters of Muqtada al-Sadr, 48, an influential Shi'ite cleric who commands the loyalty of hundreds of thousands of Iraqis. Here are some facts on Sadr.

Conflicting reports on al-Sadr’s whereabouts have been exchanged for days. In Iran, there was no word from the government or media on Mr. al-Sadr’s whereabouts. The brother of the cleric regarded as ...