US troops from the 172nd Stryker Brigade who have been redeployed from the northern city of Mosul, began appearing on Baghdad's streets on Saturday.
Some 50,000 Iraqi and US soldiers have been put on the streets of the city as part of an operation aimed at ending the sectarian bloodshed that has left thousands of Iraqis dead.
Last month, the US signalled that it was abandoning plans to cut the number of its troops in Iraq by the end of the year, and prolonged the 172nd's one-year tour by four months.
Elsewhere in Iraq the violence that the US troops are trying to end continued.
Iraqi police said they found nine bodies on Saturday that were shot in the head and bore evidence of torture.
Seven more bodies, four of them decapitated, were found by police in different parts of the southern city of Kut on Friday.
The US military confirmed that two of its soldiers were killed in action on Friday in the western city of al-Anbar and fighters killed Ali Hussein, a human rights activist, near his house in the city of Diwaniya.