Pentagon spokesman John Kirby said at a news conference that the US stands shoulder to shoulder with its NATO allies and the situation near Ukraine’s border demands that Washington reinforces "the deterrent and defensive posture" on NATO's eastern flank.

He said 1,000 soldiers, currently based in Germany, will be repositioned to Romania in the coming days to augment 900 US forces that are already there.

"This force is designed to deter aggression and enhance our defensive capabilities in frontline allied states," said Kirby.

Approximately 2,000 troops will be moving from the US state of North Caroline to Poland and Germany.

"The 82nd airborne division is deploying components of an Infantry Brigade Combat Team and key enablers to Poland and the 18th Airborne Corps is moving a joint task force capable headquarters to Germany," said Kirby.

"I want to be very clear about something. These are not permanent moves. They are moves designed to respond to the current security environment," he said.

The Wall Street Journal first reported the moves, citing US officials.

Officials told the newspaper that the Pentagon might make other moves of forces inside Europe besides ordering several thousand other troops to be on standby to deploy. The actions are intended to deter Moscow from attacking Ukraine and avert war in Eastern Europe, said the officials.

Biden said last week he would send American troops in "the near term" to NATO countries in Eastern Europe and the Pentagon put 8,500 troops on heightened alert to reinforce allies.

The US and Western allies accuse Russia of preparing for an invasion of Ukraine after Russia has reportedly amassed more than 120,000 troops on its border with the former Soviet republic alongside a mass deployment of tanks and artillery.

A similar buildup has been seen in Belarus, just north of Ukraine.

In both cases, Russia denies it is preparing an invasion and maintains its forces are there for regular exercises.

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