Article published on the 2008-04-20 Latest update 2008-04-21 15:29 TU
Another eight people were killed in clashes overnight, according to Iraqi security and medical officials.
The mosque messages repeated Sadr's call for US-led force to lift the Sadr City siege, warning of an all-out war if this is not followed.
Al-Sadr's message also called on the Iraqi army "not to fight your brothers."
In a surprise visit on Sunday, US Secretary of State Condoleezza Rice went to Baghdad. She is in the region for conferences with Gulf States.
UN and Iraqi forces are building a wall through Sadr City to stop militias from firing rockets into the Green Zone, where the US embassy and the seat of the Iraqi government is located.
The wall will be made of cement blocks stacked up to three metres high, enclosing the southern section in order to control access to and from the area, said a US military spokesman.