"We have sent forces to Europe to defend NATO territory," National Security Advisor Jake Sullivan said.
The United States said Sunday it was not sending troops to start a war with Russia after deploying 3,000 additional soldiers to Germany and Eastern Europe over the Ukraine standoff with Moscow.
President Joe Biden "has been clear for months now that the United States is not sending forces to start a war or fight a war with Russia in Ukraine," National Security Advisor Jake Sullivan told Fox News Sunday.
"We have sent forces to Europe to defend NATO territory."
Sullivan told Meet the Press on NBC that "a military escalation and invasion of Ukraine could happen at any time.
"We believe that the Russians have put in place the capabilities to mount a significant military operation into Ukraine, and we have been working hard to prepare a response," he said.
"President Biden has rallied our allies. He's reinforced and reassured our partners on the eastern flank, he's provided material support to the Ukrainians, and he's offered the Russians a diplomatic path."
Ukraine on Sunday insisted the chance of resolving the soaring tensions with Russia through diplomacy remained greater than that of an attack.
US officials have warned that the Kremlin has assembled 110,000 troops along the border with its pro-Western neighbor but intelligence assessments have not determined if President Vladimir Putin has actually decided to invade.
Officials briefed Congress and European allies in recent days that the Russian force amassed on the frontier is growing at a rate that would give Putin the firepower he needs for a full-scale invasion -- some 150,000 soldiers -- within a few weeks.
They said Putin wants options at his disposal, ranging from a limited campaign in the pro-Russian Donbas region of Ukraine to a full-scale invasion.
Russia denies that it is planning an incursion into Ukraine.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)