Germany will send up to 350 more soldiers to Lithuania to help bolster the NATO alliance's eastern flank, Defence Minister Christine Lambrecht said Monday, amid fears that Russia could invade Ukraine.

"We are therefore strengthening our troop contribution on NATO's eastern flank and sending a clear sign of our resolve to our allies," Lambrecht said, adding that the soldiers will be deployed "within a few days".

The message to allies is "you can rely on us," said the minister.

Germany currently has 500 soldiers stationed as part of NATO forces in Lithuania.

The boosted German force in the Baltic nation would make Lithuania Germany's second biggest deployment after Mali. 

Berlin had come under fire over its refusal to send weapons to Ukraine despite repeated requests from Kiev.

Its offer instead to dispatch 5,000 helmets was widely ridiculed recently.

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

An intense round of diplomacy is ongoing in a bid to stop the situation from spiralling out of control.

German Chancellor Olaf Scholz is in Washington for talks with US leader Joe Biden, while Foreign Minister Annalena Baerbock is in Kyiv for a meeting with her Ukrainian counterpart.