Ukraine has accused Russia of blocking its access to the sea as Russia prepares for naval exercises next week amid spiralling tension in the region.
Ukrainian Foreign Minister Dmytro Kuleba said the Sea of Azov was completely blocked and the Black Sea almost fully cut off by Russian forces.
Russia has repeatedly denied any plans to invade Ukraine despite massing more than 100,000 troops at the border.
But it has just begun massive military drills with neighbouring Belarus.
Belarus is a close ally of Russia and has a long border with Ukraine.
France called the drills – believed to be Russia’s biggest deployment to Belarus since the Cold War – a “violent gesture”. Ukraine says they amount to “psychological pressure”.
The US on Thursday urged Americans in Ukraine to leave immediately due to the “increased threats of Russian military action”.
“Those in Ukraine should depart now via commercial or private means,” the state department said in an advisory.
Meanwhile, UK Prime Minister Boris Johnson said that Europe faced its biggest security crisis in decades amid the tensions.
Russia’s naval exercises will take place next week in the two seas to the south of Ukraine, the Black Sea and the Sea of Azov. Russia has issued coastal warnings citing missile and gunnery firing exercises.
Ukraine’s foreign ministry said the “unprecedentedly vast area where the manoeuvres will be conducted makes navigation in both seas practically impossible”, and Defence Minister Oleksiy Reznikov tweeted that the international waters of the two seas had been blocked by Russia.
Meanwhile, the US embassy in Ukraine, tweeted that that “under the pretext of military exercises, Russia restricts Ukraine’s maritime sovereignty, limits freedom of navigation in the Black Sea/Sea of Azov, & impedes maritime traffic essential to Ukraine’s economy”.