The US will withdraw more than a third of its troops from Iraq within week.
Gen Kenneth McKenzie told reporters the troop presence would be reduced from about 5,200 to 3,000 during September.
Those remaining will continue to advise and assist Iraqi security forces in “rooting out the final remnants” of the jihadist group Islamic State, IS.
Last month, US President Donald Trump reaffirmed that he planned to pull all troops out of Iraq as soon as possible.
He is expected to hail the reduction of forces as progress towards his 2016 election campaign promise to disentangle the US from “endless wars”.The presence of US troops has also become a major issue in Iraq since the US killed top Iranian general Qasem Soleimani in a drone strike in Baghdad in January.