BAGHDAD (AP) -- A Shiite militant group threatened U.S. interests in Iraq on Thursday as part of the backlash over an anti-Islam film it described as "heinous."
Iranian-backed Asaib Ahl al-Haq leader Qais al-Khazali said the amateurish video that ridicules Prophet Muhammad was unforgiveable. A statement by the militia called on all Muslims to "face our joint enemy."
"The offense against the Messenger will put all the American interests Iraq in danger. We will not forgive that," al-Khazali told The Associated Press in an interview.
The Messenger is a reference to Muhammad, who is believed in Islam to be God's messenger.
The U.S. Embassy in Baghdad remains the world's largest American diplomatic mission, with an estimated 15,000 employees. Asaib Ahl al-Haq, or Band of the People of Righteousness, led deadly attacks against U.S. troops before the American military withdrew from the country last year. Iraqi and U.S. intelligence officials have estimated that Iran, the regional Shiite power, sends the militia around $5 million in cash and weapons each month.
The warning capped a day of growing tensions in Baghdad, where hundreds of Shiite followers of the anti-American cleric Muqtada al-Sadr demanded the closure of the U.S. Embassy in Baghdad over the anti-Islam movie.
Protestors burned American flags and carried banners reading, "We reject the attack on the Prophet Mohammed."
"No, no, to Israel! No, no to America!" thousands shouted in the Shiite stronghold of Sadr City in northeast Baghdad. "Yes, yes for Messenger of God!"
In an interview, Sadr supporter and cleric Sheikh Ali al-Atwani said the Iraqi government should shut down the U.S. Embassy in Baghdad immediately, "and the American government should apologize to the entire Islamic world."
There was no immediate response Thursday from the U.S. Embassy in Baghdad.
A leading Iraqi lawmaker also called on Washington to punish the filmmakers, saying the movie seeks "inciting violence and extremism, creating hatred among the peoples, and even inciting sectarian violence among Muslims."
But Ali al-Alak, the Shiite head of parliament's religious committee, urged Muslims worldwide to use "wise methods" in responding to it instead of turning to violence like the kind this week that killed four Americans at the U.S. consulate in Benghazi, including U.S. Ambassador to Libya Chris Stevens
Protesters in Egypt and Yemen also scaled the walls at the U.S. embassies in the capitals of those two nations.
"We regret the violence that led to the killing of U.S. diplomats in Libya, and we call for self-restraint in order not to be drawn into worldwide conflict," al-Alak said during a Thursday meeting of parliament.
Even so, he denounced the film as an "immoral act and a flagrant violation against our religion and great prophet."
Great Britain's top diplomat, Foreign Minister William Hague, told reporters in Baghdad that security at U.K. embassies in Iraq and across the Mideast is "under constant review" and condemned the Benghazi attack. Hague was meeting with parliament Speaker Osama al-Nujaifi during a brief visit to Iraq.
"Nothing is achieved by these deaths of people," he said.
But the militia called the film a "heinous act." Officials believe there are fewer than 1,000 Asaib Ahl al-Haq militiamen, and their leaders live in Iran.
"We call upon all Muslims to denounce differences to unify and face our joint enemy who targets Islam," the group said in a statement.