U.S. Secretary of Defense Lloyd J. Austin III on Thursday spoke by phone with Ukrainian Minister of Defence Andrii Taran to discuss the regional security situation amid a rise of Russian-backed separatist aggression in eastern Ukraine. Although Kremlin press spokesman Dmitry Peskov said that "it should not worry anyone and does not pose a threat to anyone" this is the most concerning move in the area since the Russians annexed Crimea in 2014.
"Additionally, we are aware of Ukrainian military reports concerning Russian troop movements on Ukraine's borders".
United States forces in Europe are now on higher alert, citing "escalations of Russian aggression" in the area.
Ukraine demanded on Thursday that Russian Federation halts escalating military tensions and reaffirms its commitment to a ceasefire in the eastern Donbass region.
"There is increased activity on the perimeter of Russia's borders by North Atlantic Treaty Organisation, other alliances, individual countries - it all obliges us to be vigilant", said Peskov.
Washington had pledged on Thursday to stand by Ukraine in the event of Russian "aggression", after Zelensky accused Russia of massing troops on the border.
"As for the participation of Russian troops in the armed conflict on the territory of Ukraine, Russian troops have never taken part in it, ' he said".
Russia's military manoeuvres came a week after four Ukrainian troops were killed in fighting in eastern Ukraine.
In addition, Secretary Austin reiterated the US commitment to building the capacity of Ukraine's forces to defend more effectively against Russian aggression.
Separately, the military announced that a Ukrainian soldier was wounded in an attack it blamed on separatists.
What is the scale of Russian involvement?
Ukraine has been battling pro-Russian separatists in the eastern Donetsk and Lugansk regions since 2014, following Moscow's annexation of the Crimean peninsula after an uprising that ousted Ukraine's Kremlin-friendly president Viktor Yanukovych.
The rebels in the Donbas region of eastern Ukraine also rely on Russian help.
The call, which was Biden's first conversation with Zelensky since his inauguration in January, came after Russian Federation warned the West earlier Friday against sending troops to Ukraine to buttress its ally. At the same time, Russian-backed forces in certain districts of Donetsk and Luhansk regions continue to violate the ceasefire.
Russian social media in recent days has been flooded by unverified videos, showing large quantities of personnel, tanks and other vehicles on the move in the country's south and south-west bordering on Ukraine.
Khomchak said this week that 28,000 separatist fighters and "more than 2,000 Russian military instructors and advisers" are now stationed in eastern Ukraine. Russian officials have not confirmed that, nor given any precise figures.
Khomchak said this week that 28,000 separatist fighters and "more than 2,000 Russian military instructors and advisers" are now stationed in eastern Ukraine.
Ruslan Khomchak, chief of the general staff of the Ukrainian Armed Forces, this week said that more than 2,000 Russian military instructors and advisers were now stationed in eastern Ukraine.