Russian special forces storm three Ukrainian Navy ships sailing through disputed waters off Crimea

Russia reopened the Kerch Strait near Crimea to shipping in the early hours of Monday morning, a day after its coast guard vessels opened fire and seized three Ukrainian navy vessels as they sailed through disputed waters around Crimea, raising fears of a new regional crisis.

Nato and the European Union issued demands for restraint after Ukraine accused Russian FSB border guards of damaging two armoured artillery boats and injuring six crew members.

All three of its vessels were immobilised and stormed by Russian special forces, the Ukrainian defence ministry said.

The FSB confirmed it seized the ships, claiming they had sailed illegally into Russian territorial waters.

“Weapons were used with the aim of forcibly stopping the Ukrainian warships,” it said in a statement circulated to Russian state media. 

Ukraine denied its ships had done anything wrong and accused Russia of military aggression.

Petro Poroshenko, the Ukrainian President, has asked parliament to vote on Monday on whether to impose martial law on the country for 60 days, after his Military Cabinet recommended the move in a late-night meeting.

Throwing his weight behind the measure, which is far from guaranteed to pass, he said it "in no way means that Ukraine will carry out any offensive actions".

"I want to emphasise separately that we have all irrefutable evidence that this aggression, this attack on the Ukrainian Navy's warships was not a mistake, not an accident, but a deliberate action," he said in a statement.

The United Nations Security Council is due to discuss the developments on Monday at the request of Russia, said Deputy Russian UN Ambassador Dmitry Polyanskiy.

The European Union said in a statement it expected Russia to restore freedom of passage via the Kerch Strait and urged both sides to act with the utmost restraint to de-escalate the situation. 

German Foreign Minister Heiko Maas on Monday called Russia's blockade of access to the Sea of Azov "unacceptable" and urged an easing of tensions with Ukraine.

"The developments are troubling," he tweeted. "A Russian blockade of the passage to the Sea of Azov is unacceptable. It is important that the blockade be lifted. We call on both sides to deescalate."

About 50-100 people gathered outside the Russian Embassy in Kiev to protest against Moscow's actions. An embassy vehicle was set on fire, according to reports.

Russia seized Crimea in 2014 and strengthened its grip by building a road bridge connecting the peninsula to southern Russia across the Kerch Strait, a narrow stretch of water linking the Black Sea to the Sea of Azov, which is home to two of Ukraine’s most important ports.

The result is an uneasy tension between the two countries as Russia tries to increase its control of the waters around Ukraine.

The seizure of its vessels came at the end of a day of mounting tension, beginning in the Kerch strait when three Ukrainian vessels tried to pass from the Black Sea into the Sea of Azov.

The Ukrainian navy said a Russian border guard ship, the Don, rammed and damaged a tug boat as the flotilla approached the strait in the morning.

Shipping in both directions was later suspended when Russia moved a large cargo ship under the arch of the Kerch bridge.

Russian military ships were deployed near the bridge over the strait and military helicopters and fighter jets were seen patrolling overhead throughout in the day.

Russian state media cited Alexei Volkov, the director of the Crimean Sea Ports, saying the closure was for “safety reasons”.

Ukraine's defence ministry accused Russia of “openly aggressive actions against Ukrainian naval ships,” and said Russian helicopters had also flown on an attack course at the vessels.

Russia's FSB, which runs the country's border guards, said the Ukrainian vessels “illegally entered a temporarily closed area of Russian territorial waters” and accused Kiev of failing to notify Russia about the ships' movements in advance.

“Their aim is clear: to create a conflict situation in this region,” the agency said in a statement.

The three Ukrainian vessels were being sent from the Black Sea port of Odessa to Mariupol, a key strategic port in Eastern Ukraine.

Russia has claimed waters around Crimea since it annexed the peninsula from Ukraine in 2014.

Its sovereignty over the peninsula and the surrounding waters is not recognised by Ukraine or Western countries.

Though a 2003 treaty designates the Kerch Strait and Sea of Azov as shared territorial waters, Russia has been asserting greater control over the passage since 2015. 

A Nato spokeswoman called for de-escalation.

“We call on Russia to ensure unhindered access to Ukrainian ports in the Azov Sea, in accordance with international law,” she said.