Rebel Shia Muslim cleric Moqtada a-Sadr urged his followers to keep fighting US forces even if he was killed or captured.
"Keep fighting even if you see me a prisoner or a martyr. God willing you will be victorious," the anti-US cleric said in a statement.
Sadr said he still wanted Iraq to remain united and thanked "those who tried to resolve the crisis peacefully".
Sadr's Mehdi Army militia has been battling US-led forces in central and southern Iraq for a week, including the holy city of Najaf, which has come under bombardment.
