Russia has confirmed its vessels have used weapons to stop Ukrainian ships that had entered Russian waters in the Black Sea illegally. Three Ukrainian sailors were wounded and have been given medical assistance.

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.

While both Russia and Ukraine have freedom of navigation in the Kerch Strait under a 2003 treaty, there are detailed technical rules on how vessels should pass through the narrow, complex waterway. Because all traffic in the area is controlled by the Crimean sea port of Kerch, every ship should contact the facility, report her route and destination, and receive permission to sail through the Strait.

The three Ukrainian vessels – the ‘Berdiansk’, the ‘Nikopol’ and the ‘Yany Kapu’ – were ignoring "legal demands to stop" and "performing dangerous maneuvers," and the Russian warships had to open fire to force them to stop, the FSB says. The ships were then seized and towed to the Crimean port of Kerch.

Read more

Three Ukrainian sailors, injured in the altercation, were given medical assistance by Russian servicemen. Their lives are out of danger.

Russia has launched a criminal investigation of the border breach.

Following the clash at sea, Ukrainian President Petro Poroshenko proposed to declare martial law in the country. The proposal has been approved by the Ukrainian National Security Council, and will go before parliament on Monday for final approval.

NATO has urged both parties to show restraint. NATO spokesperson Oana Lungescu said in a statement that NATO has been “closely monitoring developments in the Azov Sea and the Kerch Strait,” while voicing support to Ukraine.

“NATO fully supports Ukraine’s sovereignty and its territorial integrity, including its navigation rights in its territorial waters,” the statement read.