Baghdad, Iraq ? The U.S. command announced Saturday that it was sending 3,700 troops to Baghdad to try to quell the sectarian violence sweeping the capital, and a U.S. official said more American soldiers would follow as the military gears up to take the streets from gunmen.

The 172nd Stryker Brigade, which had been due to return home after a year in Iraq, will bring quick-moving, light-armored vehicles to patrol this sprawling city of 6 million people, hoping security forces respond faster to the tit-for-tat killings by Shiite militias and Sunni Arab insurgents.

The U.S. military hopes more armor will intimidate gunmen, who in recent weeks have become more brazen in their attacks.

“This will place our most experienced unit with our most mobile and agile systems in support of our main effort,” said Gen. George W. Casey Jr., the top U.S. commander in Iraq. “This gives us a potentially decisive capability to affect security in Baghdad.”

President Bush said this week that he had decided to send more troops to Baghdad after the surge in reprisal killings began to threaten the unity government of Prime Minister Nouri al-Maliki, which took power May 20.

The wave of violence has dashed administration hopes for substantial reductions in the 127,000-member U.S. mission in Iraq before the November midterm elections.

According to the U.N., about 6,000 Iraqis were killed in insurgent or sectarian violence in May and June.

The U.S. statement did not say when the Stryker Brigade would move to the capital from its base in Mosul, 225 miles northwest of Baghdad, but the redeployment was expected soon.

A U.S. military official told The Associated Press that more troops will follow the Stryker brigade, normally based at Fort Wainwright, Alaska. The official gave no further details and spoke on condition of anonymity for security reasons.

Pentagon officials have said plans call for adding military police, armored vehicles and tanks to the streets of the capital to work alongside Iraq’s U.S.-trained police and army units. Those units are heavily Shiite, and the presence of Americans is intended to assure Sunnis that the Iraqi forces are not Shiite death squads in uniform.

In other violence:

¢ The U.S. command said three U.S. Marines were killed Thursday in western Iraq.

¢ A Sunni cleric from a tribe opposed to al-Qaida in Iraq was killed in Samarra, 60 miles north of Baghdad, police said.

¢ Gunmen assassinated the western regional commander of the Iraqi Border Protection Force, Brig. Gen. Jawad Hadi al-Selawi, in Karbala, 50 miles south of Baghdad, police said.