The U.S. military says the number of its troops in Iraq is now less than 50,000, the lowest level since the U.S.-led invasion in 2003.
The announcement comes ahead of an August 31 deadline to switch the U.S. mission in Iraq from combat to training and counter-terrorism.
President Barack Obama had promised the lower levels shortly after taking office. He also reaffirmed a prior agreement to remove all U.S. troops by the end of next year.
But the terms appear to be somewhat fluid. U.S. troops were still manning key positions in Baghdad this year, long after the June 2009 announcement they had withdrawn for Iraqi cities.
Peter Harling, a senior analyst on Iraq with the International Crisis Group, based in Syria, says "I'm not sure you can draw a line very clearly between combat troops and troops conducting an advisory mission. I think Americans will remain armed and very vigilant when it comes to their own security. But indeed there is no doubt that the U.S. wants to withdraw. I think, U.S. policy in Iraq boils down to withdrawal; there's not much more to it than bailing out."
U.S. popular support for the war has fallen over the years, as casualties mounted and no clear victory appeared in sight.
Tuesday's announcement coincides with Iraq's continued struggle to form a new government, five months after inconclusive elections.
Harling says that many of the basic questions about a post-invasion Iraq remain unresolved, including power sharing, and the clearly-defined role of the military, the constitution and various branches of government.
"You can add to that, obviously, relations between Sunnis and Shi'ites, Arabs and Kurds, Iraq and all its neighbors - none of these questions have been answered," added Harling. "So withdrawing at a high pace, within the context of a framework which gives the U.S. very little flexibility, when all these questions remain unanswered is obviously a gamble."
A recent increase in violence has raised fears that the U.S. drawdown, along with Iraq's political vacuum, could further embolden insurgents.
U.S. officials said last week that they will increase the number of private security forces in Iraq by as many as 7,000. The duties of the temporary contract workers would include protecting U.S. officials.