About 3,500 American soldiers who were part of last summer's troop "surge" are scheduled to leave Iraq in the coming weeks, the U.S. military said.

The soldiers, part of the 3rd Heavy Brigade Combat Team, will redeploy to Fort Benning, Georgia, said a statement released late Monday. The U.S. sent some 30,000 additional troops into Iraq last summer to help stem growing violence.

Those troops, along with the rise of Sunni fighters who allied with the U.S. and began battling al-Qaida and a truce called by a key Shiite militia, were credited with a sharp decrease in violence during the last 10 months.

The soldiers are part of the third of five "surge" brigades scheduled to redeploy. The other two are expected to return to the U.S. by the end of July.

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

The so-called "pause" in the further redeployment of U.S. troops was pushed by Gen. David Petraeus, the top U.S. commander in Iraq, when he spoke before Congress last month.

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.

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 the northern city of 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.