Baghdad, Iraq (CNN) -- Tens of thousands of demonstrators in eastern Baghdad marked the eighth anniversary of the fall of Saddam Hussein's regime with a protest Saturday against the American troop presence there.

The demonstrators, followers of anti-American Shiite cleric Muqtada al-Sadr, rallied in Mustansriya Square, where they called all U.S troops to withdraw from Iraq at the end of the year.

The protesters carried Iraqi flag and banners, with some chanting "Baghdad is a free country, America get out!" and "No for Occupation, No for America."

One banner read "No, no America," while another said, " Yes, yes for Quran."

American troops are scheduled to depart from Iraq at year's end under a bilateral agreement between the Iraqi government and the United States.

But if violence increases and instability persists in Iraq, it is possible both countries could agree to keep some U.S. troops in Iraq, which now has about 47,000 American soldiers. The figure is down from a high of 171,000 in 2003.

That prospect of American troops staying in Iraq disturbs many citizens, including the thousands who support al-Sadr, a cleric with grassroots appeal in Iraq's Shiite cities and neighborhoods.

Sheikh Salah al-Obaidi, a cleric who read a statement to demonstrators on behalf of al-Sadr, raised the prospect of American troops staying in Iraq into next year and beyond.

"What if the invading forces decide not to leave our country? What if they decide to stay? What if American troops and others decide to stay in our lands? .... Will you keep silent? " al-Obaidi said, reading al-Sadr's statement to chants of "God is great."

"If they decide to stay in our country, then we have to do two things: first is to escalate armed resistance and lift the freeze on Mehdi Army," al-Obaidi said.

He was referring to the August 2007 suspension of the activities of the Mehdi Army, al-Sadr's militia.

U.S. military commanders have cited that move as a major reason for a decline in violence across Iraq, where Al-Sadr's forces fought American troops during the height of the war.

Emotions on the street were fueled by the remarks of U.S. Defense Secretary Robert Gates, who made an unannounced visit this week to Iraq and discussed American troop presence with top officials, including Prime Minister Nuri al-Maliki.

"My message to them was if there is to be a presence or they still need help, we are open to that possibility. But they have to ask, and time is running out in Washington because we have a lot going on around the world and we've got to make some decisions," Gates said.

"It obviously would be a presence that's a fraction of the size of the one we have here now but it's really up to the Iraqis at this point."

On Friday, street protesters in Baghdad and other provinces also focused on the fall of the Hussein regime and grievances stemming from war, including an opposition to the U.S. troop presence.

That was a change of theme in recent weeks when demonstrators in Iraq have rallied over the same bread-and-butter issues that have prompted street protests across the Arab world.

People have been upset over corruption, unemployment, the lack of basic services and restrictions on freedom of expression.

Protesters in the Sunni neighborhood of Adhamiya called for the release of detainees and compensation for "the victims of the occupation."

"Some of the protesters shouted, 'No to occupation, no to foreign troops,'" witnesses said.

In Baghdad's Tahrir Square, nearly 300 protesters carrying banners and Iraqi flags, shouted, "We will not accept life in an occupied country anymore."

One of the banners read, "No to American and Iranian occupation!" That includes a reference to Iran's influence with the Shiite masses and the Iraqi government.

Women carried pictures of their sons and husbands who are missing or were killed during the war.

"During this war, so many women lost sons and many others became widows, not only Iraqi women but also American women. We are the ones who paid the price of this war," said Shima Kareem, who was among the protesters.

Hundreds also turned out in Falluja, in the largely Sunni Anbar province in the west and in Samarra, in Salaheddin province in the north to demand the release of detainees, compensation for victims' families, and the departure of American troops.

Since 2003, 4,421 U.S. troops have died in Iraq, according to the military figures counted by CNN.

A U.S.-led invasion of Iraq in March 2003 led to the removal of Saddam Hussein's regime on April 9. The iconic toppling of the former ruler's statue in Baghdad's Firdous Square symbolizes the regime's fall.