U.S. soldiers sent to reinforce security in Baghdad were seen for the first time on the streets of the capital, as six people were killed in Iraq's ongoing sectarian and political violence, officials said Sunday. As many as 3,700 soldiers of the Army's 172nd Stryker Brigade were sent from the northern Iraqi province of Nineveh to bolster U.S. and Iraqi security forces that are struggling to contain the violence in Baghdad. Several Stryker armored fighting vehicles were seen Saturday in Baghdad's neighborhood of Ghazaliyah, the Associated Press reported. Iraqi police used loudspeakers to encourage residents to reopen their shops and go about their business normally because the soldiers would protect them. Another U.S. command, the 3rd Stryker Brigade of the 2nd Infantry Division, was sent from its home base of Fort Lewis in Washington state to replace the 172nd, said a U.S. spokesman, Lt. Col. Edward Loomis. He said the 3rd Brigade's units have been replacing counterparts in the 172nd over the last month, and resumed full responsibility of Nineveh on Saturday.