Joe Biden voiced Washington's support for Ukraine in a phone call Friday with the Ukrainian president, as Russian Federation builds up its military presence along the border.
"What we would object to are aggressive actions that have an intent of intimidating, or threatening, our partner Ukraine", State Department spokesman Ned Price told reporters.
Talks with Russian President Vladimir Putin in Paris in December 2019 brought the sides no closer to a lasting settlement.
"Secretary Austin reaffirmed unwavering USA support for Ukraine's sovereignty, territorial integrity, and Euro-Atlantic aspirations".
Ukraine's military intelligence accused Russian Federation of preparing to "expand its military presence" in the separatist-controlled regions.
A high-ranking Ukrainian government official, speaking on condition of anonymity, claimed that the Russian army was practicing "military coordination" with separatists.
More than 50 battalion combat teams comprising 15,000 people will take part in those exercises and practice "interaction with electronic warfare and air defense units", the defense military told reporters.
On Wednesday, the Pentagon said US forces in Europe had raised their alert status following the "recent escalations of Russian aggression in eastern Ukraine".
The conflict in eastern Ukraine - which broke out in 2014 following Ukraine's pro-Europe Maidan revolution and Russia's annexation of Crimea - has seen repeated flare-ups since a ceasefire was brokered in 2015, but the warnings and statements coming from Moscow, Kiev and Washington are the most serious and strongly worded in months.
Despite several different videos showing trains full of armored vehicles streaming toward the border, Moscow is insisting that it is not sending troops to reinforce the separatists in the Donbass.
He added that "it should not worry anyone and does not pose a threat to anyone".
Ukrainian war veterans march as Nationalists movements demonstrate in front of President Volodymyr Zelensky's offices in Kiev in October past year. Chairman of the Joint Chiefs, General Mark Milley has met with his Ukrainian counterpart and discussed the issue.
On Thursday, the deputy head of Zelensky's office, Roman Mashovets, called for joint drills with North Atlantic Treaty Organisation forces to "help stabilize the security situation".
Zelenskiy was elected in 2019 on promises of ending the conflict, but critics say a shaky ceasefire was his only tangible achievement.
Since 2014, the United States has committed more than $2 billion in security assistance to Ukraine, including a recently announced $125 million package that featured defensive weapons and other key capabilities to enhance the lethality, command and control, and situational awareness of Ukraine's Armed Forces.