According to Moscow,  in November 2018, in the same area, two small Ukrainian armored artillery vessels and a tugboat had entered its territorial waters illegally, a statement that Ukraine denied. Whatsoever, the Navy opened fire on them, wounding several sailors and eventually seizing the vessels.

What is more, in May, the International Tribunal for the Law of the Sea (ITLOS) has ordered Russia to 'immediately' release 24 Ukrainian sailors who were seized along three naval ships off Crimea in November.

The Ukrainian vessels had tried to pass through the Kerch Strait, the only access to Ukrainian ports on the Sea of Azov. But Russia has controlled the Strait since annexing Crimea, and its Coast Guard boats fired on the vessels before boarding them, BBC reported.

In July, Ukraine seized a Russian tanker moored in a river port near the Black Sea, in retaliation for Russia’s seizure of three Ukrainian vessels and arrest of 24 sailors in November 2018. According to Ukraine’s SBU security service, the country seized the Russian tanker 'Nika Spirit' in Izmail.

According to the Guardian, Russia threatened to retaliate as well, if arrests were made, but according to a spokesman for the Russian embassy in Kyiv, the crewmembers were then heading back to Russia.