On Thursday, Ukraine's security service seized Russian tanker Neyma, which Ukraine believes took part in the incident in the Kerch Strait near Crimea in November 2018.

Russia seized at the end of November three Ukrainian ships near Crimea in an incident that risked spilling over into a wider conflict between the two countries, exacerbating the disputes between Moscow and Kiev over oil and gas resources and infrastructure.

Russia—which annexed Crimea in 2014, for which the U.S. and the EU imposed sanctions on Moscow—said at the time that three Ukrainian vessels had violated its state border in waters near Crimea.

Ukraine, for its part, said that it had informed Russia about the plans for the ship movements and said that the seizing of the vessels was "another act of armed aggression" by Russia.

The November 2018 incident was the first open conflict between Russian and Ukrainian militaries in recent years. Tensions had been rising over the access to the Kerch Strait, where the incident took place, and the Sea of Azov.