As many as 8,500 US troops have been put on heightened alert for a possible deployment to Eastern Europe as Russian troops mass on Ukraine's border, Pentagon spokesman John Kirby said Monday, CNN reported.

US Secretary of Defense Lloyd Austin issued the prepare to deploy orders at the direction of President Joe Biden, the latest step the US has taken to prepare for a potential Russian invasion of Ukraine that officials have warned could be imminent.

As of Monday afternoon, no final decision to deploy the troops had been made, Kirby emphasized.

Earlier on Monday CNN reported the Biden administration was in in the final stages of identifying specific military units it wants to send to Eastern Europe, according to multiple US and defense officials.

Biden discussed options for bolstering US troop levels in the Baltics and Eastern Europe with his top military officials during a briefing at Camp David last Saturday, according to a senior official.

Biden held an 80-minute secure video call with European leaders on Monday afternoon, which the White House said was part of the administration's consultation and coordination with European allies in response to Russia's military buildup.

The objective of sending US troops to Eastern Europe is to provide restraints to the allies and calm them down.

But there is no assumption that American troops will be deployed in Ukraine, or take part in any military action.