"Russia remains a threat today, tomorrow and in the foreseeable future for the whole of Europe," Finnish Prime Minister Petteri Orpo told reporters following the first Eastern Flank Summit gathering the leaders of Bulgaria, Estonia, Finland, Latvia, Lithuania, Poland, Romania and Sweden.

"Russia's war of aggression against Ukraine and its repercussions constitute a profound and enduring threat to European security and stability," a final declaration signed by the leaders stated.

"The situation calls for an immediate prioritisation of the EU's eastern flank through a coordinated and multi-domain operational approach," it said.

That includes "ground combat capabilities, drone defence, air and missile defence, border and critical infrastructure protection, military mobility and counter mobility", they said.

Europe's Eastern Flank is a common responsibility and "must be defended with urgency, leadership and resolve," they said.

The efforts should be coordinated with NATO, they added.

"The EU can play an important role in supporting member states' individual efforts to strengthen their defence capabilities by defining financing, by simplifying regulations and strengthening military mobility," Swedish Prime Minister Ulf Kristersson said.

"The EU and NATO have obviously different important but very complementary roles in relation to the eastern flank."

Tuesday's declaration comes as Ukraine, backed by European countries, tries to reach a compromise with the United States on a proposal to end the war, of which the initial version was deemed favourable to Moscow.