US President Donald Trump has repeatedly criticised NATO, and insisted that European allies take more responsibility for its defence by boosting military spending as Ukraine battles Russia's invasion.

This latest announcement came after reports earlier this year that Washington could withdraw 10,000 troops from eastern Europe, which analysts have said could embolden Moscow.

Romania's Defence Minister Ionut Mosteanu however said the decision was not a "withdrawal".

It was the "cessation of the rotation of a brigade that had elements in several NATO countries, including Bulgaria, Romania, Slovakia and Hungary", he told journalists after the ministry statement was released.

The statement itself said "the resizing of US forces" was a result of the "new priorities of the presidential administration, announced back in February".

It added that 1,000 US soldiers would remain deployed in Romania.

They will help "to deter any threat" and represent "a guarantee of the United States' commitment to regional security", said Mosteanu.

According to the latest government figures, about 1,700 US troops are currently deployed in Romania.

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

- 'Weaken security' -

A NATO official told AFP that the body had been informed by the administration of US President Donald Trump in advance, and played down its significance.

"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 the alliance remained "clear", the official added.

Mosteanu insisted that strategic capabilities were "unchanged", adding that "the missile-defence system at Deveselu 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 Romania, which is a "frontline state", 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.