evidence: Ukraine says the move violated the 2003 agreement between the two nations on treating the Sea of Azov and the Kerch Strait as shared waters without any restrictions. [...] The strait that connects the Black Sea to the Sea of Azov has significant political, military and economic importance for Ukraine. Losing access to it would cut off the ports of Ukraine’s Mariupol and Berdyansk cities from the Black Sea, essentially turning the Sea of Azov into a backwater for the country.