The waters near the Crimean peninsula were the site of a tense standoff between Russian and Ukrainian ships that involved a chase, some gunfire, and fighter jets, followed by strong statements from Moscow and Kiev.
The Ukrainian vessels were sailing between two Ukrainian ports: from Odessa in the Black Sea to Mariupol in the Azov Sea. The only waterway that connects the two is the Kerch Strait between Crimea and mainland Russia. Kiev says it has notified Moscow in advance that its navy ships would be sailing through the area. Moscow denies it had been given the warning.

At around 7am Moscow time (4am GMT) on Sunday, two artillery boats and a tugboat belonging to the Ukrainian Navy crossed the Russian maritime border in the Black Sea and headed to the Kerch Strait.

Vessels generally pass through the strait after proper notification and according to a schedule, but these ships had not followed the procedure, according to Russian Federal Security Service responsible for maintaining order at the border.

[link to www.rt.com (secure)]