Ukraine's Foreign Minister Dmytro Kuleba on Saturday slammed Germany for its refusal to supply weapons to Kyiv, urging Berlin to stop "undermining unity" and "encouraging Vladimir Putin" amid fears of a Russian invasion.

With tens of thousands of Russian troops massed on the Ukrainian border, fears are mounting that a major conflict could break out in Europe.

Ukraine's calls to Western allies to bolster its defense capabilities have seen the United States, Britain and Baltic states agreed to send to Kyiv weapons, including anti-tank and anti-aircraft missiles.

Kuleba said on Twitter that Germany's statements "about the impossibility of supplying defense weapons to Ukraine" did not match "the current security situation."

Ukraine's minister stressed that "today the unity of the West in relation to Russia is more important than ever."

"The German partners must stop undermining unity with such words and actions and encouraging (Russian President) Vladimir Putin to launch a new attack on Ukraine," Kuleba said.

Ukraine is "grateful" to Germany for the support it has already provided, but its "current statements are disappointing," he added.

Earlier on Saturday German Defense Minister Christine Lambrecht said that Berlin will send a field hospital to Ukraine, while once again rejecting Kiyv's calls for weapons.

Berlin has already delivered respirators to Ukraine and severely injured Ukrainian soldiers are currently being treated in Bundeswehr hospitals, she told Welt am Sonntag newspaper.

"Weapons deliveries would not be helpful at the moment – that is the consensus within the government," Lambrecht said.

Moscow insists it has no plans to invade Ukraine but has at the same time laid down a series of security demands – including a ban on Ukraine joining NATO – in exchange for de-escalation.