BAGHDAD, Iraq (CNN) -- Iraqis outraged by a proposed security pact between Iraq and the United States staged an angry but peaceful protest against the deal Friday.

Protesters demonstrate Friday in downtown Baghdad against a deal to keep U.S. forces in Iraq.

Thousands of people -- most of whom are backers of anti-American Shiite cleric Muqtada al-Sadr -- streamed into Baghdad's Firdous Square waving Iraqi flags, hoisting posters with portraits of the cleric and carrying signs scorning the agreement.

Protesters at one point set fire to U.S. flags and an effigy of President Bush, but the rally was well-organized and peaceful with no evidence of fighting or arrests. People dispersed amicably after the 2½-hour event.

The protest was announced last week by al-Sadr, who called for Sunnis and Shiites to hold a unified Friday prayer ceremony and have a peaceful demonstration against the agreement.

The security agreement, reached after months of negotiations between Iraqi and U.S. representatives, sets June 30, 2009, as the deadline for U.S. combat troops to withdraw from all Iraqi cities and towns. The date for all U.S. troops to leave Iraq would be December 31, 2011. Watch what happens to an effigy of President Bush »

It would replace a U.N. resolution expiring at year's end that sets out the role of U.S. and allied troops in Iraq.

The Iraqi government approved the pact Sunday, and now the measure is under debate in parliament, where there has been overheated discussion between proponents and opponents. A vote is expected next week.

The Sadrists have long been in the forefront of opposition to the deal, and others -- such as Sunni Arabs and secularists -- have expressed reservations and opposition to the pact.

The Sadrists oppose having any agreement with the United States and want U.S. forces to leave immediately. They have been protesting the security agreement for months in Baghdad's Sadr City, where the cleric has strong support.

The demonstration brought out one of the largest crowds to congregate in Baghdad since protests against the agreement started this year.

The square was sealed off and traffic was blocked as thousands chanted "No no to the agreement," "No no America," and "Out, out occupation."

The effigy of Bush had been hanging next to a monument in the square where a statue of deposed Iraqi President Saddam Hussein was toppled in April 2003 during the U.S.-led invasion of Iraq.

Protesters eventually pulled down the hanging effigy, threw shoes at it, stomped it and burned it.

Al-Sadr wasn't at the demonstration and is believed to be in Iran.

A sheikh at the protest, Abdul Hadi al-Mohamadawi, read a letter from al-Sadr. He renewed his rejection of the agreement and called on followers to use means they deem appropriate to get the "occupier" out of Iraq.

Prime Minister Nuri Al-Maliki's government approved the security pact earlier in the week. Parliament has wrestled with the proposal for several days and may vote on it Monday.

If a vote has to be held beyond Monday, Kurdish lawmaker Mahmoud Othman said it could be delayed by the annual hajj religious pilgrimage and Eid al-Adha, the Muslim holiday that comes at the end of the pilgrimage.

Othman said about 50 lawmakers plan to attend the hajj on Tuesday or Wednesday.

Al-Maliki warned on Thursday that if the measure isn't approved, there won't be enough time to develop a new agreement before the year is out.

He said the country might have to delay its quest for sovereignty and ask the U.N. Security Council to renew a resolution that authorizes the presence of U.S. and allied troops in Iraq.

Other developments

• A roadside bomb detonated near an Iraqi police checkpoint in southern Baghdad on Friday, killing three people and wounding 15 others, an Iraqi Interior Ministry official said. Four police officers were among the wounded in the capital's Dora district.

• A second roadside bombing took place in western Baghdad's Mansour district, the official said. The bomb targeted an Iraqi army foot patrol, wounding two soldiers and two civilians.

• In southern Baghdad on Friday, the U.S. military reported three bombings in the Hadar neighborhood of southern Baghdad. One person was killed and four others were wounded.

• The military also reported the non-combat death of a U.S. soldier in the northern Iraqi city of Mosul on Friday, bringing the number of U.S. service member deaths this month to 13.

All About Iraq • U.S. Armed Forces • Muqtada al-Sadr • Nuri al-Maliki