The United States yesterday said it was in discussions with its Nato allies over Russia's military build-up near the Ukrainian border as fresh reports showed ballistic missiles arriving in the region.
Jen Psaki, the White House press secretary, said that Washington was "increasingly concerned" about what has been described as Russia's largest military manoeuvres in the area since the break-out of hostilities in eastern Ukraine in 2014.
"Five Ukrainian soldiers have also been killed this week alone. These are all deeply concerning signs."
Russia's military build-up was first reported last month as social media footage showed an unusually large number of tanks, troops and other equipment moving across the country to the south and the southwest.
Fighting between Russian-backed separatists and Ukrainian government troops first broke out following Moscow's 2014 annexation of Crimea but subsided in recent years.
Janes, a military analysis group, said that its experts have identified the Iskander short-range ballistic missile systems among Russia's most recent deployment in the Voronezh region. It also reported that tanks and artillery units had been deployed to the area which now houses a field hospital and a large communications system.
Volodymyr Zelenskiy, the Ukrainian President, yesterday flew to the frontline where he handed out awards to Ukrainian soldiers clad in a helmet and bulletproof vest.
"Thank you for keeping people calm and protecting our land. You are a real example of heroism and dedication," Zelenskiy told them.
His visit came two days after he asked Nato to speed up his country's request to join the alliance.
Angela Merkel, the German Chancellor, who has previously taken an active role in mediating the conflict, phoned Vladimir Putin, the Russian President, and "demanded that this build-up be unwound in order to de-escalate the situation", according to her office.
The Kremlin has rejected the accusations of whipping up tensions, claiming that its deployment was purely defensive.
However, Dmitry Kozak, chief negotiator in relations with Kyiv and Moscow-backed separatists said that Russia could be "forced" to defend its citizens in eastern Ukraine under certain circumstances.
He warned that an escalation in the conflict would be "the beginning of the end of Ukraine", describing that scenario for the ex-Soviet country as "not a shot in the leg, but in the face".
President Joe Biden has previously affirmed the US's "unwavering support" for Ukraine's sovereignty and territorial integrity.