BAGHDAD —  About 3,500 American soldiers are scheduled to leave Iraq in the coming weeks, the U.S. military announced, part of a plan to reduce the number of troops who were part of last year's "surge" by 20,000.

The soldiers, part of the 3rd Heavy Brigade Combat Team, will redeploy to Fort Benning, Ga., the military said.

The U.S. sent some 30,000 additional troops into Iraq last year to help stem growing violence. The troop increase, a truce by a key Shiite Muslim militia and the rise of Sunni fighters who allied with the U.S. in the battle against Al Qaeda were credited with a sharp decrease in bloodshed during the last 10 months.

The soldiers are part of the third of five "surge" brigades scheduled to leave the country. The other two are expected to return to the U.S. by the end of July, leaving an estimated 140,000 troops in Iraq after a peak of more than 160,000.

"The continued drawdown of surge brigades demonstrates continued progress in Iraq," Brig. Gen. Dan Allyn said in the statement released late Monday. "After July, commanders will assess our security posture for about 45 days and determine future force requirements based on these conditions-based assessments."

Gen. David Petraeus, the top U.S. commander in Iraq, has pushed for a so-called "pause" in further redeployment of U.S. troops.

Critics have called for a quicker withdrawal of American soldiers, but commanders on the ground insist the slowdown is needed so a sharp increase in violence is not seen when U.S. forces leave.

Separately, the U.S. military said in a statement Tuesday that a brothel in northern Iraq was attacked the day before. The Americans blamed the attack on Al Qaeda insurgents, but local police did not speculate on who carried out the killings.

Iraqi police said the attack in Mosul killed three prostitutes and wounded two others.

There have been a string of attacks against women deemed immoral in recent months, including the bombing of hair styling salons and the frequent murder of women not wearing traditional clothing in the southern city of Basra.

Meanwhile, at least four civilians were killed overnight in the Baghdad Shiite neighborhood of Sadr City, hospital officials said Tuesday. Some 21 people were injured at the same time in Sadr City, which has seen fierce fighting between the Mahdi Army militia and U.S. and Iraqi troops.

Clashes in the sprawling slum of 2.5 million people that serves as a power base for radical Shiite cleric Muqtada al-Sadr and his Mahdi fighters have raged for five weeks, since the Iraqi government began a crackdown on the militants in southern Iraq.

Hassan al-Rubaie, a Sadrist lawmaker, suspended his seat in parliament on Tuesday to protest the fighting in Sadr City. He said he held the government of Prime Minister Nouri al-Maliki responsible for the fighting in the slum.

The lawmaker also blamed Iran for interfering with Iraq's security and said the neighboring nation was causing much of the violence by supplying money, weapons and training to Iraqi fighters, a charge U.S. commanders have repeatedly made. Iran denies the allegations.

Meanwhile, U.S. and Iraqi forces raided two police stations and arrested 48 policemen suspected of having links to Shiite militias late Monday in the Baghdad neighborhood of Shula, a Shiite stronghold, a policeman said on condition of anonymity as he was not authorized to speak to the media.

Elsewhere, two policemen were killed Monday night in clashes with unidentified gunmen in Mosul, a provincial policeman said on condition of anonymity as he was not authorized to speak to the media. Around the same time in eastern Mosul, two gunmen were killed by police.