About 1,000 US troops stationed in Germany will be moved eastward to Romania while 2,000 more will deploy to Poland and Germany from the United States -- reportedly from Fort Bragg military base in North Carolina.

"These forces are not going to fight in Ukraine," stressed Pentagon spokesman John Kirby.

"They are not permanent moves. They respond to current conditions," he added, referring to Russia's placement of more than 100,000 troops along with heavy offensive weapons along Ukraine's border.

Both Romania and Poland border Ukraine, a former Soviet state that is facing Russian aggression which has sent tensions between Washington and Moscow soaring to their highest levels since the Cold War.

A US official said the move by the Pentagon was seen as a repositioning of certain Europe-based units further east, while forward-deploying extra US-based units to Europe and maintaining the "heightened state of readiness of response forces" to meet commitments to NATO.

The West has warned that a Russian attack would be met with "severe consequences" including wide-ranging economic sanctions.

Russian President Vladimir Putin on Tuesday accused the West of ignoring Moscow's security concerns and of using Ukraine as a tool to contain Russia, though he said he hoped a solution could be found to end spiralling tensions.