Russia is said to have closed almost 70 percent of the Sea of Azov around the annexed Ukrainian peninsula of Crimea for military exercises.
The Russian fleet is apparently planning target practice in front of the Ukrainian ports of Mariupol, Berdyansk and Henichesk, Kiev naval forces announced on Friday.
A confirmation from the Russian side was initially not available.
The previous day, the Russian border guards accused a ship of the Ukrainian Navy of approaching the Kerch Strait without permission. The leadership in Moscow spoke of a dangerous provocation. Kiev rejected the charge. The ship “Donbass” did not leave its own territorial waters. The Sea of Azov is a common inland sea between Russia and Ukraine and is only connected to the greater Black Sea by the Kerch Strait.
In November 2018, three Ukrainian military ships were hijacked by the Russian border guards while attempting to cross this strait.
The 24 sailors were only released after months of negotiations.
The incident worsened relations between the two ex-Soviet republics.
Ukraine has been at war with Russia since its neighbor first annexed Crimea in 2014 and then supported eastern Ukrainian separatists in Donbass.