The Russian coastguard opened fire on two artillery boats and a tug belonging to Ukraine which it claimed had made an unauthorised passage through Russia’s waters.
Two of the craft, the Berdyansk and the Nikopol, were damaged and six crew members injured.
The confrontation took place near the hotly contested Kerch Strait, which separates the peninsula from the Russian mainland.
Russia’s FSB security service confirmed its border patrol boats had seized the Ukrainian naval vessels in the Black Sea and used weapons to force them to stop, Russian news agencies reported.
The FSB said it had been forced to act because the ships had illegally entered its territorial waters, attempted illegal actions, and ignored warnings to stop while manoeuvring dangerously.
“Weapons were used with the aim of forcibly stopping the Ukrainian warships,” the FSB said in a statement circulated to Russian state media.
“As a result, all three Ukrainian naval vessels were seized in the Russian Federation’s territorial waters in the Black Sea.”
Ukrainian authorities said they had given advance notice to the Russians that the vessels would be moving through the strait.
The incident prompted Petro Poroshenko, the Ukrainian president, to push parliament to declare martial law after convening a meeting of his war cabinet.
He said the parliament could decide on Monday whether to approve martial law, which would restrict civil liberties and give state institutions greater power.
The Independent has contacted the FSB and Russia’s defence ministry for comment.
The Kerch Strait is the only passage into the Sea of Azov. The strait is spanned by the recently completed Kerch Bridge, connecting Crimea to Russia. Transit under the bridge has been blocked by a tanker ship, and dozens of cargo ships awaiting passage are stuck.
A 2003 treaty designates the Kerch Strait and Sea of Azov as shared territorial waters but Russia has been asserting greater control over the passage since 2015 – the year after it illegally annexed Crimea. Moscow also backed a pro-Russia insurgency in eastern Ukraine.
Russia has not given any indication of how long it will block the strait, but a long-term closure to would amount to an economic blockade of Ukrainian cities on the Azov coast. Russia’s Black Sea Fleet greatly outmatches the Ukrainian navy.
Nato said it “fully supports Ukraine’s sovereignty and its territorial integrity, including its navigational rights in its territorial waters”. A spokeswoman added: “We call on Russia to ensure unhindered access to Ukrainian ports in the Azov Sea, in accordance with international law.”
Additional reporting by agencies
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