The US military has put 8,500 troops on alert to deploy to Europe at short notice to bolster NATO efforts on the continent.
This is the latest sign of US resolve in the face of Russian military build up on the border of Ukraine and Pentagon spokesperson John Kirby stressed no decision whether to deploy or not had been made yet.
The troops could be called on in case of an escalation between Ukraine and Russia.
Kirby added that any deployment would separate from intra-European movements of U.S. troop to NATO's eastern flank, to reassure nervous allies.
This comes as defence chiefs finalise plans to bring home up to 1,000 Britons from Ukraine fears of a Russian invasion intensify.
Officials are considering sending troops from 16 Air Assault Brigade to mount an evacuation of UK nationals.
The same unit helped with the rescue mission in Kabul last summer, when the Afghan city was overrun by the Taliban.
Defence sources say troops would fly to Ukraine in RAF transports and help pull out expats.
Russia have amassed over 100,000 troops on the border of the Eastern European country, escalating a crisis which has been unresolved since 2013.
Around 30 members of the SAS, the SBS and the Special Reconnaissance are believed to have been in the region for several weeks now.
Britain has also sent 2,000 light anti-tank weapons along with a team of 30 soldiers from the Ranger Regiment.
Despite a strong response this time around, some have said that a weak response to Putin's previous aggressions may have given him the green light for an invasion this time.
Colonel Richard Kemp, a former infantry commander, told the Mirror: “He learnt this when he invaded the Crimea with no real consequences and when his nerve gas and polonium attacks in Britain received little effective counter-action.
“It was confirmed by NATO’s abandonment of Afghanistan to the Taliban.”
Russia has long denied planning an invasion, despite engineering a crisis on the border.
Moscow has claimed the western response proves that Russia is the target of aggression, not instigator of it.
As tensions continue to rise, Britain confirmed it was withdrawing some staff and dependants from its embassy in Ukraine.