"We must send a clear message on behalf of the EU that we will support Ukraine and that Russia's aggressive action will face a tough response," the president said.
During the phone conversation, Nauseda and Von Der Layen discussed the tense security situation in the region – Russia's military buildup near Ukraine's border and also in the territory of Belarus, the presidential press service said.
The Lithuanian president said Russia's growing military forces in Belarus are raising concern, adding that the key task now is to deescalate the existing security situation.
The unity of the European Union and NATO allies, solidarity with and support to Ukraine are now key as geopolitical tensions rise, the Lithuanian leader said.
He also welcomed the EC's decision to allocate 1.2 billion euros in financial assistance to Ukraine.
Russia now has more than 100,000 troops and military equipment near its border with Ukraine, with the West increasingly concerned that a major military conflict might break out in Europe. Moreover, Russia has recently been moving its troops to Belarus near the EU border for planned joint army drills.
As tension continues to rise over Russia's military buildup, NATO allies announced on Monday they are putting forces on standby and sending additional ships and fighter jets to NATO deployments in eastern Europe.