The Permanent Court of Arbitration will in June hear Russia's objections against a move by Ukraine to drag it before the world' oldest arbitration body over rights to coastal waters around annexed Crimea.
Russia snatched the Black Sea peninsula from Kiev in 2014 and was being accused by the West of illegally blocking access to the Sea of Azov, used by both Russia and Ukraine.
Kiev in September 2016 dragged Moscow to the Hague-based PCA, saying it instituted arbitration under international maritime laws "to vindicate its rights as the coastal state in maritime zones adjacent to Crimea in the Black Sea, Sea of Azov and Kerch Strait."
It asked the arbitral tribunal to "enforce its maritime rights by ordering the Russian Federation to cease its internationally wrongful actions in the relevant waters."
Kay Bailey, the US ambassador to NATO added that allies would send more ships to the area to ensure that "countries in and around the Black Sea are safe from Russian meddling."
Moscow in turn criticised the Black Sea plan, saying it regretted that the alliance "has no intention to renounce its political and military confrontation with Russia" asking instead to de-escalate "military and political tensions."