WASHINGTON

Roughly 8,500 Americans troops have been put on heightened alert in the US in case NATO activates its Response Force or if the security situation in Europe deteriorates further, the Pentagon said on Monday.

John Kirby, the Defense Department spokesman, said the troops are primarily ground forces who could bring a host of capabilities to the European theater if needed, including logistics, medical, aviation, intelligence, surveillance and reconnaissance, transportation.

"The decision now has been made to put these units on higher alert, and higher alert only. No decisions have been made to deploy any forces from the United States at this time," said Kirby. "The United States will maintain close coordination with allies and partners as we continuously review our force posture and make decisions regarding movement of forces in to and within Europe.”

The decision to put the forces on standby comes amid growing tensions in eastern Europe as the West and NATO accuse Russia of preparing for an invasion of Ukraine. Russia has amassed over 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 to the north of Ukraine. In both cases, Russia denies preparing for an invasion, and maintains its forces are there for regular exercises.