An image released by the Crimean Branch of the Russian Federal Security Service apparently shows three Ukrainian vessels as Russian ships close in. (Photo: TASS)

The incident sharply escalated tensions that have been growing between the two countries since Moscow annexed Crimea from Ukraine in 2014. Russia has since worked steadily to bolster its zone of control around the Crimean Peninsula. The Ukrainian navy says Russian ships fired on and seized two of its artillery ships. A tugboat was also seized, and two crew members were wounded.