The Ukrainian navy threatened to shoot Russian coast guard vessels near the Kerch Strait just hours before Putin closed the waterway to foreign warships in the latest sign of mounting tensions in eastern Europe.
The standoff took place between three Ukrainian Gyurza-M-class artillery boats and five unidentified vessels belonging to Russia's FSB coast guard service overnight between Wednesday and Thursday, according to Black Sea News editor Andrii Klymenko who monitors military activity in the area.
Russian vessels began making 'provocative manoeuvres' around the Ukrainian boats and only backed off after they threatened to open fire, Mr Klymenko reported. The incident happened within 25 miles of the Kerch Strait.
The incident has echoes of a 2018 clash between Ukraine and Russia in the strait which led to three Ukrainian ships being captured and Russia blocking the strait using a large container ship, sparking a diplomatic crisis.
Just hours after the latest incident took place, Russia again announced that it was closing the strait to foreign warships until October - ostensibly so that naval training exercises can take place.Ukraine has branded the move a violation of its rights.
The move cuts off the Sea of Azov to the outside world including the Ukrainian port cities of Mariupol and Berdiansk, which border the Donbas region where fighting is currently taking place between Russian-backed rebels and Ukrainian forces.
It also makes it much harder for Ukraine's allies to ship supplies and reinforcements to the disputed region, should Moscow decide to march troops that it has been massing along the border into Ukraine.
There are now more than 80,000 Russian soldiers in the region along with thousands of tanks and vehicles, amid warnings that number could top 115,000 by next week.
Three Ukrainian artillery boats threatened to shoot five FSB coast guard vessels near the Kerch Strait overnight between April 14 and 15, observers said, after the Russian ships made 'provocative manoeuvres'
A photo believed to have been taken on board one of the Ukrainian vessels on the night in question shows a sailor on deck with what appears to be a cargo vessel in the background
The Ukrainian vessels were Gyurza-M-class artillery boats (file image) taking part in a routine patrol when they were confronted by the Russian coast guard
The move came just hours before Putin closed off the Kerch Strait to foreign warships, which Ukraine said violated its right to navigation under a UN treaty - and which cuts off the disputed border region from supplies coming via sea
Putin moved to close the strait after Joe Biden slapped sanctions on Moscow for what he said were Russian attempts to interfere in US elections and a large hack of US government data.
Biden called the move 'proportionate' and said he could have gone further, but chose not to in an effort to maintain 'a stable predictable relationship' with Russia and to avoid 'a cycle of escalation and conflict'.
Earlier in the day, the president had called off two US destroyers which had been sent towards the Black Sea as a warning to Russia, while calling for 'de-escalation' and dialogue between the two sides.
Biden had proposed holding a summit with Putin in a neutral country in the coming months to discuss the issues facing the two countries, including tensions in Ukraine, but has not yet received a response.
As the diplomatic tussle between the US and Russia plays out, Ukrainian president Vlodomyr Zelensky was today meeting with European allies in Paris as a show of strength to Russia and to secure concrete support as he tries to fend off the threat of invasion.
French President Emmanuel Macron will meet with Zelensky in person, while German Chancellor Angela Merkel will join via videolink.
'Ukraine's sovereignty is under threat,' Macron's office said, adding: 'All our work is aimed at avoiding an escalation and defusing tensions.'
Zelensky's meeting with the leaders of France and Germany, who have been mediators in the conflict since 2015, comes as Ukraine accuses Russia of threatening to destroy it.
'They are openly threatening Ukraine with war and the destruction of Ukrainian statehood,' Foreign Minister Dmytro Kuleba told a press conference with counterparts from the fellow former Soviet countries of Estonia, Latvia and Lithuania.
Putin is continuing to build up his forced on the border with Ukraine, as the government warns troops numbers could swell to 110,000 with 7,000 tanks and other vehicles in support
Russian mobile artillery (left) and support vehicles continue to move to the front lines, videos published today showed
Russian tanks are seen moving towards the border region on the back of a train filmed in the Krasnodar region of Russia today
'The red line of Ukraine is the state border. If Russia crosses the red line, then it will have to suffer,' he warned.
Meanwhile Britain's ambassador to Moscow arrived at the Russian foreign ministry for talks on Friday after London summoned the Russian ambassador, the RIA news agency reported, amid a further deterioration in bilateral ties.
Britain's foreign ministry said on Thurday it had summoned Russia's envoy to express its concern about 'malign behaviour' by Moscow and to show London's support for sanctions announced earlier in the day by Biden.
The British embassy told RIA the meeting at the foreign ministry had been planned in advance.
It comes as Ukraine has warned that it could unilaterally build a nuclear arsenal if NATO refuses to permit it membership of the Western military alliance.
It was formerly a nuclear state with 176 ICBMs and 44 strategic bombers after the collapse of the Soviet Union in 1991, and agreed to eliminate its weaponry in return for legally-binding security guarantees from Britain, the US and Russia.
'We must do everything possible to ensure that [Russian President Vladimir] Putin will not attack us tomorrow or the day after tomorrow,' said Andriy Melnik, Ukraine's ambassador to Germany.
'The only possibility for this is for Ukraine to finally become a NATO member.
'If Ukraine were a NATO member in 2014... it would never have come to the annexation and this terrible war in the east,' he said.
He warned bluntly: 'Ukraine has no other choice - either we are part of an alliance such as NATO and are doing our part to make this Europe stronger, or we have the only option – to arm by ourselves, and maybe think about nuclear status again.
'How else can we guarantee our defence?'
In a plea for the West to bolster its security guarantees he said: 'Almost 90,000 (Russian) servicemen, as well as their armed systems were pulled to the border and to the region of occupied Crimea and Donbas.
'This deployment is not just muscle flexing...
'We are dealing with the largest troop movement in Russia since the Second World War.'
The latest incident echoes a confrontation between the Russian and Ukrainian navies in the Kerch Strait in 2018 which saw Russian vessels ram their Ukrainian counterparts and take them captive
The 2018 incident led to Russia blocking the Kerch Strait with a large container vessel, sparking a diplomatic crisis
Russian state-owned Sputnik news agency said in a report that Ukraine 'likely retains the technical capability to build a nuclear arsenal'.
But it said: 'The state of its civilian nuclear power programme leaves something to be desired.
'Last year, Ukrainian nuclear industry workers sounded the alarm about the threat of 'another Chernobyl' citing a 'dire situation' which they said was 'taking shape in the country's nuclear energy sector' due to a lack of oversight, safety permits, and funds.'
Kyiv warned strongly over the threat of the Azov Sea tension escalating into a major incident.
'Russia continues to violate international law,' said the Ukrainian navy
'Russia's FSB made yet another attempt to hinder the lawful actions of a Ukrainian Navy boat group on combat duty.
'The Ukrainian Navy's tactical boat group proceeded with its mission despite Russian provocations and deliberate efforts to restrict free navigation.'
On Thursday Ukraine issued a protest over Russia's decision to bar foreign warships and state vessels from parts of the Black Sea in the direction of the Kerch Strait from next week until October.
Ukraine's foreign ministry said: 'Such actions by the Russian Federation are another attempt, in violation of the norms and principles of international law, at usurping (our) sovereign rights as a littoral state.
'It is Ukraine that has the right to regulate navigation in these parts of the Black Sea.'
There were claims that satellite images show Russia has installed in Crimea S-400 anti-aircraft systems with a range of 250 miles, according to Information Navigator.
This allows 'the Russian occupation forces to control almost all the airspace of the Black Sea'.
Meanwhile, new videos show continued Russian troop movements east of the Ukrainian border.