Moqtada Sadr supporters want US-led forces out of Iraq
At least 20 people have been killed and more than 100 injured in clashes between Spanish-led troops and Iraqi demonstrators in the city of Najaf.
Four soldiers from El Salvador and two from Iraq were reportedly killed in the firefight, which broke out when Shia protesters marched on their base.
The crowd were protesting in support of firebrand cleric Moqtada Sadr.
The US administrator in Iraq, Paul Bremer, said protesters had "crossed the line and moved to violence".
The BBC's Barbara Plett in Baghdad says the clashes marked the most serious confrontation between the occupation forces and members of Iraq's Shia majority.
