American flags were set on fire Friday to chants of "no, no for occupation" as followers of an anti-U.S. Shiite cleric marked the sixth anniversary of the Iraq war.
An aide to cleric Muqtada al-Sadr also called on supporters to join an April 9 march that will demand Americans leave Iraq. Baghdad fell to U.S. forces on April 9, 2003.
The war began with a missile and bombing attack on south Baghdad before dawn on March 20, 2003 - March 19 in Washington.
"Today, a remembrance of the cruel occupation of Iraq, and on April 9, there will be a chant for liberation," al-Sadr aide Sheik Haidar al-Jabiri told worshippers gathered in Baghdad's Shiite district of Sadr City for Friday sermons.
He added: "Sayed Muqtada invites you to march by the millions on April 9, the anniversary of the cruel occupation."
A similar planned march last year was canceled. Al-Sadr's previous demonstrations have attracted thousands of supporters, but have not reached 1 million.
Demonstrators responded by lifting a banner reading: "To the Iraqi government, when you will be trustful and release our detainee sons?"
"No, no for occupation. Yes, yes for liberation. Yes, yes for Iraq," the demonstrators chanted.
Two American flags were set on fire.
Among other Iraqis, however, the 6th anniversary comes at a time of increased optimism about the future. A survey of 2,228 Iraqis questioned nationwide last month for ABC News, BBC and Japan's NHK, found that 85 percent believed the current situation was good or very good - up 23 percent from last year.
While violence still continues at levels that most other countries would find alarming, the country is much safer than 2007, when sectarian bloodshed peaked.
Tenuous truces among tribal factions have aided the situation, but there is no guarantee they will provide lasting stability,.
The protest came a day after a U.S. airstrike on a militant hideout north of Baghdad killed at least 11 insurgents, the U.S. said.
A search of the site by ground forces after the strike found a cache of weapons, munitions and parts to build improvised explosive devices, U.S. military spokesman Maj. Derrick Cheng said Friday.
Cheng did not immediately know Friday whether any civilians were killed or injured in the strike, or exactly when it occurred. He said the suspected insurgents were hiding near several bunkers south of Balad Ruz in Diyala province - about 45 miles northeast of Baghdad.
An Iraqi security official, speaking on condition of anonymity because he was not authorized to talk to the media, said the strike took place Thursday morning.
Meanwhile, the U.S. military announced the Thursday death of an American soldier from non-combat causes in Iraq.
A statement issued Friday did not identify the soldier, or give any details about where or how the death occurred. It said the soldier's division operates in an area south of Baghdad.
At least 4,260 American service members have died in Iraq since the war started, according to an Associated Press count.