Iraqi Shia cleric Moqtada al-Sadr has called for a million-strong demonstration against US "occupation".
The demonstration would take place next Wednesday, the fifth anniversary of the fall of Baghdad, when the US commander in Iraq is scheduled to brief Congress in Washington about progress in the war.
"The time has come to express your rejections and raise your voices loud against the unjust occupier and enemy of nations and humanity, and against the horrible massacres committed by the occupier against our honourable people," said a statement released by Sadr's office in the holy city of Najaf.
The statement called on Iraqis of all sects to descend on Najaf, site of annual Shia pilgrimages that frequently attract hundreds of thousands of worshippers.
US forces called in helicopter strikes during a clash with gunmen today in the city of Hilla and bombed a house in Basra overnight, stepping up raids after days of relative calm that followed a truce announced by Sadr on Sunday.
Sadr has millions of followers and was able to summon tens of thousands of people onto the streets in Baghdad for demonstrations during fighting last week, but a march to Najaf would potentially mobilise entire swathes of Shia Iraq.
The cleric also called for a "peaceful sit-in" in Baghdad tomorrow to protest against bombings, arrests and vehicle bans that continue to seal off parts of the capital.
Iraq's worst fighting since at least the first half of last year mainly ended on Sunday after Sadr called his followers off the streets. But Sadr supporters say government forces are still rounding them up and besieging Sadr strongholds in Baghdad.