In Baghdad, hundreds of protesters gathered in Sadr's stronghold of Sadr City, holding up posters of Sadr, burning U.S. flags and chanting, "Death to America". They condemned the blasphemous movie Innocence of Muslims.
"How long will we stay in this coma where there is no real sanction?" Sheikh Riyadh al-Waeli, a Sadr aid, told protesters. "This demonstration is not enough unless there is a real sanction."
The crowd in Basra also numbered in the hundreds and both Sunni and Shi'ite clerics participated in the demonstration, which was organized by Sadr's office.
"We have to fire the U.S. ambassador because these things are carried out under U.S. supervision and are aimed at offending Islam and Muslims," protester Yaarab al-Mohammadawi said.
Another protest also took place in the city of Najaf, 160 km (100 miles) south of Baghdad.
Iraqi Prime Minister Nuri al-Maliki denounced the film as "insulting" and "racist" but called on Muslims not to react with violence.
"The natural response is to refrain from resorting to violence and demonstrate the principles of Islam and its civilized values," he said in a statement on Thursday.
Thousands of protesters, both Shi'ite and Sunni, marched through the southern port city of Basra on Friday, burning U.S. and Israeli flags.
The demonstration was led by the Supreme Islamic Iraqi Council (SIIC), one of Iraq's largest and most powerful Shi'ite political parties.
Tribal leaders in Basra said they wanted the U.S. missions shut down, while Sheik Abu Kifah al-Bakhatri also called for a boycott of U.S.-made goods.