Roughly 8,500 American troops have been put on heightened alert in the U.S. in case NATO activates its Response Force amid tensions in Ukraine, the Pentagon said on Monday.
US Department of Defense spokesman John Kirby said the troops are primarily ground forces.
They bring a host of capabilities, including logistics, medical, aviation, intelligence, surveillance, and reconnaissance, as well as transportation.
Tensions are growing in eastern Europe as the West and NATO accuse Russia of preparing for an invasion of Ukraine.
Russia has allegedly amassed more than 120,000 troops on its border with the former Soviet republic according to American sources.
Ukraine however maintains that there is no unusual activity at the Russian border.