Hundreds of thousands of Iraqi Shias have demonstrated in the holy city of Najaf, calling for US-led troops to leave Iraq.
The protesters were responding to an appeal by cleric Moqtada Sadr, who branded US forces "your arch enemy" in a statement.
The demonstration marks four years since US troops entered Baghdad and ended the rule of Saddam Hussein.
Baghdad has been placed under curfew for the duration of the anniversary.
A 24-hour ban on movement by all vehicles, for fear of car bomb attacks, began in the city at 0500 (0100 GMT) on Monday, where four years ago a giant statue of Saddam Hussein was torn down, symbolising the fall of his regime.