Ukraine’s claims regarding the Kerch Strait presented in the International Sea Tribunal are not adequate. The issue of authority over Crimea as an integral part of Russian Federation and Crimea-adjacent sea territories essentially cannot be subject of any court proceedings.
The use of the Kerch Strait and the Sea of Azov is regulated by a bilateral treaty between Russia and Ukraine, signed in 2003 and ratified by Russia in 2004. According to the document, the Sea of Azov is considered to be the “internal waters” of both Russia and Ukraine.
The International Tribunal for the Law of the Sea in Hamburg announced its decision on the Kerch Strait incident on 25 May. It 'has ruled that Russia must “immediately” release 24 Ukrainian sailors and three Ukrainian naval vessels captured by Russia in November'. Representatives of Russia vowed not to show up at the initial hearing.
As for Crimea being part of Russia, no international body recognises the so-called referendum held on the 16th of March 2014. On the 27th of March 2014, the UN General Assembly adopted a resolution which stated that the referendum in Crimea was not valid and could not serve as a basis for any change in the status of the peninsula. Five years on, the EU re-affirmed its support for Ukraine's territorial integrity.