The US reduction of troops in Iraq has been completed days before President Donald Trump leaves office.
There are now 2,500 US service members in Iraq and 2,500 in Afghanistan.
It is the lowest number of personnel in Afghanistan since military operations began in 2001.
“The drawdown of US force levels in Iraq is reflective of the increased capabilities of the Iraqi Security Forces,” acting Defence Secretary, Christopher Miller, said on Friday.
"We have long anticipated that the force level required to support Iraq’s fight against ISIS would decrease as Iraq’s capability to manage the threat from ISIS improves."
In November, Mr Trump ordered commanders to cut troop levels in Iraq to 2,500 from about 3,000.
Mr Miller said the reduction did not signify a change in Washington’s policy and is part of a plan to decrease US involvement in large operations across Iraq.
“US and Coalition forces remain in Iraq to ensure the enduring defeat of ISIS,” he said.
“The government of Iraq and the US government agree that ISIS remains a threat and that a US and Coalition presence remains vital.”
Washington will maintain “a counter-terrorism platform in Iraq to support partner forces with air power and intelligence".
Since the US-led invasion in 2003, almost 4,500 American troops have been killed and more than 32,000 injured, according to the Pentagon.
“The Iraqi people desire a secure, stable, and prosperous Iraq, able to defend itself against violent extremist groups and against those who would undermine Iraq’s security,” he said.
Mr Miller said Washington was committed to supporting those objectives.
The presence of American forces has been contested by Iraqi politicians.
The US and Iran came close to war after rocket attacks on Iraqi bases hosting American forces and US air strikes against militia groups, including one that killed Iranian general Qassem Suleimani and top Iraqi militia leader Abu Mahdi Al Muhandis on January 3, 2020, in Baghdad.
After the attack the Iraqi Parliament voted to remove all foreign troops from the country.
But some Kurdish and Sunni politicians said the expulsion of troops could leave Iraq vulnerable to an insurgency, undermine security and further empower the country's Iran-backed militias.
In Aghanistan, at a high point in 2011 there were 98,000 troops, the Pentagon said.
"Today, the United States is closer than ever to ending nearly two decades of war and welcoming in an Afghan-owned, Afghan-led peace process to achieve a political settlement and a permanent and comprehensive ceasefire," Mr Miller said.