EU foreign policy chief Josep Borrell and US Secretary of State Antony Blinken discussed Russia's military build-up around Ukraine during a telephone call Saturday.
The call came ahead of a Jan. 10 US-Russia meeting on security in Geneva.
They reaffirmed the EU and US support for Ukraine's sovereignty, independence, and territorial integrity and emphasized the need for Russia to de-escalate and fully implement the Minsk agreements, the EU said in a statement.
Any further military aggression against Ukraine will have massive consequences and severe costs, it said.
They also discussed bilateral and multilateral diplomatic engagements following the proposals presented by the Russian Federation regarding Moscow's views about the security arrangements in Europe.
They underlined the US' and the EU's enduring partnership and shared commitments to Transatlantic security and to confront common security challenges.
And they agreed that any discussion about European security will happen in coordination and with the participation of the EU and to keep in close touch on all priority areas.
Russia seized and occupied the Crimea Peninsula from Ukraine in 2014 and remains the de facto authority there. Moscow that year also began to support separatist forces in eastern Ukraine against the central government, a policy that it has maintained over the past eight years.
