The Pentagon said Monday it is putting up to 8,500 troops based in the United States on "heightened alert" for possible deployment to eastern Europe amid growing fears that Russia may further invade Ukraine.

"Even as we continue to prioritize diplomacy and dialogue, we must also increase readiness," Pentagon spokesman John Kirby told a press conference, adding that the move is intended to support the forces of the North Atlantic Treaty Organization and reassure allies, especially those located near Russia and Ukraine.

Ukrainian servicemen are seen outside of Svitlodarsk, Ukraine on Jan. 23, 2022. (Anadolu Agency/Getty/Kyodo)

Kirby said no decisions have been made to deploy any forces from the United States at this time, but the idea is that all of the units the Defense Department is putting on alert will be "ready to go on a shortened timeframe."

He also emphasized that the move does not mean "diplomacy is dead."

Russia began a massive buildup of military forces and equipment on Ukraine's border months ago, with its military presence now around 100,000 troops, according to the State Department.

Moscow has denied having any intention to invade Ukraine, from which it annexed Crimea in 2014, instead seeking to blame the escalating tensions on NATO and Ukraine, which aspires to join the alliance. Russia has also demanded security guarantees such as precluding NATO's expansion to Ukraine and refraining from military activities there.

The United States has been warning of severe economic and financial sanctions should Russia choose to invade, while calling on Moscow to de-escalate tensions.

"I don't think anybody wants to see another war in the European continent. And there's no reason why that has to occur," Kirby said. "This can be solved very easily by the Russians de-escalating by moving some of these forces away, which they haven't done."