Senior Republicans have voiced their alarm at US plans to withdraw some of its forces in Afghanistan and Iraq.
The US is to cut its number of troops in Afghanistan and Iraq by 2,500, the US Department of Defense confirmed.
President Donald Trump has long called for troops to come home and has criticised US interventions abroad.
But Senate Majority Leader Mitch McConnell – usually a staunch defender of Mr Trump – called the plan “a mistake”.
He also warned the president against taking “any earthshaking changes in regards to defence and foreign policy” before leaving office.
Mr Trump is yet to concede to Democrat Joe Biden, and the cuts are scheduled to take place five days before Mr Biden takes office on 20 January 2021.
In Iraq, the number of US troops will be cut by 500 to 2,500, while the number of service personnel in Afghanistan will fall from 4,500 to about 2,500.
Acting US Defense Secretary Chris Miller said the move reflected Mr Trump’s policy “to bring the wars in Afghanistan and Iraq to a successful and responsible conclusion and to bring our brave service members home”.
Shortly after the announcement, several rockets were fired into the Green Zone in Baghdad and landed near the US embassy. It is the first such attack since Iraqi militias linked to Iran agreed to stop targeting the embassy compound last month. There are no reports of casualties or any damage.
What are US forces doing in Afghanistan?
US forces have been in Afghanistan since 2001. A US-led coalition ousted the Taliban weeks after the 11 September 2001 attacks in the US by al-Qaeda, which was then based in Afghanistan.
The Taliban regrouped and became an insurgent force that by 2018 was active in more than two-thirds of the country.
The US started withdrawing troops from Afghanistan as part of a historic peace deal signed by the US and the militants on 29 February.
Military chiefs, including Gen McKenzie, have warned in the past that peace negotiations between the Taliban and Afghan authorities could be undermined by a hasty US withdrawal.
Why are Republicans critical?
On Tuesday, White House National Security Adviser Robert O’Brien said it was Mr Trump’s hope that “all US troops will be home from Afghanistan and Iraq by May”.
Along with Mr McConnell, several other senior Republicans also voiced their concern. Texas Republican congressman Mac Thornberry called the move a “mistake”, saying cutting troop numbers would “undercut negotiations” currently underway aiming to bring an end to fighting in Afghanistan.
And Senator Ben Sasse, who sits on Senate Intelligence Committee, said it was a “weak retreat” and that it was “not grounded in reality and will make the world a more dangerous place.”
Nato Secretary-General Jen Stoltenberg said on Tuesday that “The price for leaving too soon or in an uncoordinated way could be very high.”
In a statement, he said Afghanistan risked once again becoming a platform for international militants to organise attacks.
Acting US Defense Secretary Chris Miller did not confirm if the drawdown plan had been endorsed by Gen Mark Milley, chairman of the Joint Chiefs of Staff, but said that military commanders had agreed to execute it.
He said the US had met its goal of defeating extremists and helping “local partners and allies to take the lead in the fight”.
“We will protect our children from the heavy burden and toll of perpetual war, and we will honour the sacrifices made in the services of peace and stability in Afghanistan, Iraq and around the world,” he said.
At least one Democratic politician supported President Trump’s move. Adam Smith – the chair of the House Armed Services Committee – said it was “the right policy decision”.
“While the history of conflict in the region is complex and predates our direct involvement, after nearly 20 years of armed conflict, Americans and Afghans alike are ready for the violence to end,” he wrote in a statement.