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Image source, TASS via Getty Images

To sum up Sunday's dramatic and fast-changing events:

• In the morning, Ukraine said it had sent two gunboats and a tug from the Black Sea port of Odessa to Mariupol in the Sea of Azov

• Ukraine's navy then said Russia boats had tried to intercept its vessels, ramming the tug

• Russia accused Ukraine of illegally entering its territorial waters

• Russia scrambled fighter jets and helicopters as the Ukrainian vessels approached a bridge over the Kerch Strait - the only access to the Sea of Azov

• The bridge itself was blocked by a tanker

• In the evening, Ukraine said its vessels had been fired on and seized by the Russians. Six Ukrainian crew members were injured

• Russia confirmed it had used the weapons to force the Ukrainian vessels to stop, saying three Ukrainian sailors were injured

• Ukraine held a crisis meeting of the national security and defence council, asking parliament to back a proposal to declare martial law on Monday

The BBC's Jonah Fisher has recently spoken to commanders of the Ukrainian navy about the rising tensions in the Sea of Azov.

They say there would not be a repeat of what happened in Crimea in 2014

More from the continuing protest in front of the Russian embassy in Ukraine's capital Kiev (see our 22:16 entry).

Image source, Reuters

Image source, Reuters

Image source, AFP/Getty Images

Russian Foreign Affairs Ministry spokeswoman Maria Zakharova said Ukraine was acting like "highwaymen" in the Kerch Strait.

In a Facebook post (in Russian),, external she writes that first there was a "provocation", then "coercive pressure" and finally "the accusation of aggression".

The BBC's Kiev correspondent says imposing martial law could delay March's elections.

President Petro Poroshenko says he will ask parliament on Monday to back the proposal to declare martial law in Ukraine.

Mr Poroshenko says the measure will help strengthen Ukraine's defence, but it does not mean the declaration of war.

The crisis meeting of Ukraine's National Security and Defence Council is now under way.

Addressing the council, President Petro Poroshenko described the Russian actions as "unprovoked and crazy".

The presidential elections in Ukraine are scheduled for 31 March 2019.

Christopher Miller, a correspondent who covers Ukraine and Russia, says Sunday's events mean the loss of about a third of Ukraine's entire armed fleet.

Ukrainians have been pictured placing paper boats at the Russian embassy in Kiev, to protest against the seizure of the three navy ships.

Image source, Reuters

Image source, Reuters

Image source, Reuters

Steve Rosenberg
BBC Moscow Correspondent

Tension between Russia and Ukraine has been building for months off the coast of Crimea.

Under a 2003 treaty between Moscow and Kiev, the Kerch Straight and the Sea of Azov are shared territorial waters.

But recently, Russia began inspecting all vessels sailing to or from Ukrainian ports in the area.

The use of force by Russia to seize Ukrainian vessels - with casualties - is a major escalation.

But you won’t hear Moscow taking the blame.

Under President Vladimir Putin, when Russia has used force before, its line of defence has always been: "We didn’t start it."

That goes for the Russia-Georgia war of 2008, and the appearance of "Little Green Men" (Russian special forces) in Crimea in 2014, which preceded Moscow's annexation of the peninsula.

So expect Moscow to pin the blame for what happened on Sunday - and for whatever happens next - on President Petro Poroshenko’s government.

Image source, Reuters

Ukrainian Foreign Minister Pavlo Klimkin told a Ukrainian TV channel that "Russia has carried out an act of aggression against Ukraine."

He said he was in contact with "friends and partners" and they were drawing up a "clear sequence of actions we are going to take together".

"With this in mind, I talked today to both friends and the leadership of international organisations such as Nato and the EU. The president will shortly speak to the leadership of international organisations to build a clear-cut coalition to resist Russia's acts of aggression."

Nato spokesperson Oana Lungescu says the military alliance is "closely monitoring" developments in the Sea of Azov and the Kerch Strait.

"We call for restraint and de-escalation," she says.

"Nato fully supports Ukraine's sovereignty and its territorial integrity, including its navigational rights in its territorial waters. We call on Russia to ensure unhindered access to Ukrainian ports in the Azov Sea, in accordance with international law.

"At the Brussels Summit in July, Nato leaders expressed their support to Ukraine, and made clear that Russia's ongoing militarisation of Crimea, the Black Sea and the Azov Sea pose further threats to Ukraine's independence and undermines the stability of the broader region."

The EU says tensions have "increased dangerously", external as a result of the incident between Russia and Ukraine.

"We expect Russia to restore freedom of passage at the Kerch strait and urge all to act with utmost restraint to de-escalate the situation immediately," the EU says in a statement.

It says the construction of the Kerch bridge by Russia, under which a tanker is blocking passage through the strait, took place without Ukraine's consent and is "another violation of Ukraine's sovereignty and territorial integrity".

"The European Union expects Russia to stop the inspections. The EU does not and will not recognise the illegal annexation of the Crimean peninsula by Russia," the statement adds.

The FSB also confirms that Russia's border patrol boats used weapons to force the Ukrainian ships to stop, Ria Novosti reports.

The FSB says three Ukrainian soldiers were injured.

Ukraine's National Security and Defence Council will convene to discuss the crisis at 24:00 local time (22:00 GMT), and will propose declaring martial law, council secretary Oleksandr Turchynov is quoted as saying by Ukrainian media.

In its latest statement, the Ukrainian navy says one of its gunboats and the tug have been seized and are being towed.

Another gunboat is blocked and is being escorted by "occupants". The vessel is not damaged.

The navy says that six Ukrainian service members were injured.

Russia's state news agency Tass has published these images of the Ukrainian boats which it says had illegally crossed into Russian waters.

Image source, Tass/Getty Images

Image source, Tass/Getty Images

Image source, Tass/Getty Images