Officials were quick to downplay the reduction in personnel, which comes amid a review of US military deployments worldwide that has worried European allies concerned about President Donald Trump's commitment to the continent.

"This is not an American withdrawal from Europe or a signal of lessened commitment to NATO and Article 5," the US Army in Europe and Africa, said in a statement, referring to the alliance's collective defence principle.

Trump has repeatedly criticised NATO and insisted that Europe boosts military spending and takes more responsibility for its defence as Ukraine battles Russia's invasion.

The Pentagon says there are nearly 85,000 US military personnel in Europe -- a number that has fluctuated between 75,000 and 105,000 since Russia's 2022 invasion of Ukraine.

- 'Resizing' -

The US military said Wednesday an infantry brigade combat team and an airborne division were to redeploy to their Kentucky home base without replacement.

It was not immediately clear how many troops were concerned. A brigade usually numbers up to 5,000 soldiers.

"This force posture adjustment will not change the security environment in Europe," the US army said.

Reports earlier this year said Washington could withdraw 10,000 troops from eastern Europe as it shifts focus towards the Indo-Pacific region, which the Pentagon called its "priority theatre".

Romania's defence ministry, which previewed the pullout beating Washington to an official announcement Wednesday, said the "resizing" was the result of new US priorities and a strengthened NATO presence on the eastern flank.

It would affect a brigade with elements in several NATO countries, including Bulgaria, Romania, Slovakia and Hungary, Bucharest added.

A NATO official told AFP the alliance had been informed by the Trump administration in advance, describing the US move as nothing "unusual".

"Even with this adjustment, the US force posture in Europe remains larger than it has been for many years, with many more US forces on the continent than before 2022," the official said.

Washington's commitment to NATO remained "clear", the official added.

- 'Wrong signal' -

Romania's Defence Minister Ionut Mosteanu said 900-1,000 US soldiers would remain in the country to help "deter any threat".

According to the latest government figures, about 1,700 US troops are currently deployed in the Black Sea nation, which borders war-torn Ukraine.

But experts such as George Scutaru, co-founder of the New Strategy Center, a Romanian think tank, warned that while not significantly affecting the military balance, the move sent the "wrong signal".

"Russia will consider that Black Sea is not so important for American interests in Europe," he told AFP.

Moscow could be encouraged to pile pressure on Romania by, for example, violating its airspace with drones and other aircraft, he said.

Germany, home to the largest contingent of American troops in Europe, said it was not affected by the redeployment.

Poland's Defence Minister Wladyslaw Kosiniak-Kamysz also said the country had "not received any information... about a reduction in the contingent in Poland".

Romania's Mosteanu insisted strategic capabilities were "unchanged". He added that a missile-defence system at the Deveselu NATO base "remains fully operational".

"The Campia Turzii air base continues to be a key point for air operations and allied cooperation, the Mihail Kogalniceanu base continues to be developed, and the American flag will remain present at all three sites," he added.

"An air-combat group will remain at the Kogzlniceanu airbase, as was the case before the outbreak of the conflict in Ukraine," he said.

The US decision will however "weaken the security" of "frontline state" Romania, Phillips O'Brien, an analyst based at Scotland's University of St Andrews, warned.

"Please wake up, Europe -- the USA will not defend you against Russia," he wrote on X.

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