The narrow waterway provides access from the Black Sea to the Sea of Azov near Crimea, and the episode represents a rise in tensions between the two countries.
Deeply concerning escalation by Russia in Kerch Strait. Russia must stop its provocative behaviour and allow for maritime transport in accordance with international law. Welcome discussion in UNSC on how to avoid further escalation.— Margot Wallström (@margotwallstrom) November 26, 2018
Moscow claims the Ukrainian ships illegally entered Russian water and were planning an attack. Russia is not releasing the ships, keeping them docked in a nearby harbor.
Ukraine, for their part, says Russia broke the agreement which allows both countries territorial rights over the waterway, which is the only way out of the sea.