The United States could withdraw 10,000 troops from eastern Europe, NBC News reported, in a move some analysts fear would embolden Russia.
About 20,000 extra troops were deployed to the region in 2022 under former president Joe Biden, reinforcing NATO's eastern flank after Russia invaded Ukraine.
NBC on Tuesday cited six US and European officials confirming discussions about halving the deployment, focused on cutting numbers in Romania and Poland.
President Donald Trump is pushing for a speedy end to the more than three-year war in Ukraine since taking office but has failed to yet reach a breakthrough.
He has repeatedly criticised NATO, and insisted that Europe take more responsibility for its defence by boosting military spending and taking the lead in arming Ukraine.
Trump questions the US commitment to defending NATO allies who underpay, alarming Europe amid rising Russian assertiveness.
Any downsising of US forces would increase President Vladimir Putin's "willingness to meddle in various ways across the spectrum in Europe," Seth Jones, of the Center for Strategic and International Studies, told NBC.
About 100,000 American troops are currently stationed in Europe, with 65,000 based permanently on the continent, while the rest are rotating staff and reinforcements.
Former US president Donald Trump pushed NATO countries to pay their bills or face Russian encouragement, sparking discussions on presidential diplomacy and international relations.
