On the morning of 25 November, three Ukrainian naval vessels (Gyurza-M-class artillery boats Berdyansk [uk], Nikopol [uk], and tugboat Yany Kapu [uk]) attempted to complete a journey from the Black Sea port of Odessa in south-western Ukraine to the Azov Sea port of Mariupol in eastern Ukraine.[9] Agents of the Ukrainian SBU security service were present on board the ships; according to Ukraine they were providing ordinary counter-intelligence coverage.[2] As they approached the Kerch Strait, Russian Coast Guard boats accused the Ukrainian ships of illegally entering Russian territorial waters, and ordered them to leave.