Ukraine’s navy says Russia has fired on and seized three of its vessels off the coast of the annexed Crimea, in a major escalation of tensions.
It said two gunboats and a tug were captured by Russian special forces and six crew members were injured.
Ukraine said would meet to declare martial law over the incident.
The crisis began when Russia accused the Ukrainian ships of illegally entering its waters and stopped them from sailing into the Sea of Azov.
The Russians placed a cargo ship under a bridge in the Kerch Strait. It is the only access to the Sea of Azov, which is shared between the two countries.
Ukrainian President Petro Poroshenko called an urgent meeting of his “war cabinet” over the incident, his spokesperson said.
Tensions have recently risen in the Black Sea and the Sea of Azov off the Crimean peninsula – annexed by Russia in 2014.
How did the crisis unfold?
In the morning, Ukraine’s Berdyansk and the Nikopol gunboats and the Yana Kapa tug tried to sail from the Black Sea port of Odessa to Mariupol in the Sea of Azov.
Ukraine said the Russians tried to intercept the ships, ramming the tug. The vessels continued towards the Kerch Strait, but were prevented by the tanker.
Russia scrambled two fighter jets and two helicopters to the area. It accused the ships of illegally entering its waters said the traffic had been suspended for security reasons.
The Ukrainian navy later said the boats were hit and disabled as they tried to leave the area. It said the tug was forced to stop.
Ukraine said it had informed the Russians of its plan to move its ships through the sea to Mariupol.
What’s the background to this?
The shallow Sea of Azov lies east of Crimea, and south of the Ukrainian regions partially seized by pro-Russian separatists.
The two Ukrainian ports on its northern shore – Berdyansk and Mariupol – are key for exporting grain and produce such as steel, also for importing coal.
In 2003, Ukraine and Russia signed a treaty that defined the Sea of Azov as internal waters of the two countries. The treaty guaranteed free navigation to all Ukrainian and Russian vessels.
But Russia has recently begun inspecting all vessels going to or from Ukrainian ports. Earlier this month, the EU warned it would take “targeted measures” to address the issue.