The UK has denied claims that Russian forces fired shots at a Royal Navy destroyer in the Black Sea.
Moscow has said a Russian patrol boat fired shots towards HMS Defender and that a warplane dropped four high explosive fragmentation bombs in its path after it entered Russian waters off the coast of the Crimea peninsula.
The Russian Defence Ministry said the destroyer was "warned in advance that weapons would be fired in case of a violation of the Russian state border" and that the vessel "disregarded the warning".
“As a result of joint actions of the Black Sea Fleet and the Border Service of the Russian Federal Security Service, HMS Defender left the territorial sea of the Russian Federation," it said.
Britain has accused Russia of “disinformation” over the claim with Prime Minister Boris Johnson's spokesman saying: "It's incorrect to say either that it was fired upon or that the ship was in Russian waters."
However, BBC correspondent Jonathan Beale, who was invited aboard the British ship prior to the incident, said the Russians had harassed the vessel and that he heard shots.
“Increasingly hostile warnings were issued over the radio - including one that said ‘if you don't change course I'll fire’," he said in a report from HMS Defender's deck.
Mr Beale added: “We did hear some firing in the distance but they were believed to be well out of range.”
He said two Russian coastguard boats came within 100 yards of the ship as they shadowed it, and there were more than 20 Russian aircraft above.
Watch: UK's new aircraft carrier HMS Queen Elizabeth proves object of curiosity for Russia
HMS Defender left Russian waters soon afterwards, having ventured as much as two miles inside, Russia's defence ministry said.
"The destroyer had been warned that weapons would be used if it trespasses the border of the Russian Federation. It did not react to the warning," it said.
However, the UK's Ministry of Defence said no Russian warning shots were fired and it did not recognise assertions that bombs were put in the vessel's path.
"We believe the Russians were undertaking a gunnery exercise in the Black Sea and provided the maritime community with prior-warning of their activity," the MoD said in a statement on Twitter.
It added: “The Royal Navy ship is conducting innocent passage through Ukrainian territorial waters in accordance with international law."
Defence Secretary Ben Wallace insisted the ship had stuck throughout to an internationally recognised “traffic separation route”.
He acknowledged it had been “shadowed” by Russian forces during its transit from Odessa in southern Ukraine towards Georgia but played down the incident saying it was “routine” practice.
"These are the things that come an go with Russia. Disinformation, misinformation is something that we have seen regularly. We are not surprised by it,” he said.
“We plan for it and we take all steps to make sure we are not escalatory or provocative."
Ukrainian foreign minister Dmytro Kuleba said the incident showed that Russia's "aggressive and provocative policies" in the Black Sea and nearby Azov Sea constituted a "continuous threat to Ukraine and its allies".
In a tweet, he called for Nato to cooperate with Ukraine in the Black Sea.
Military experts said that whether or not the details of the Russian or British accounts were accurate, the incident appeared to represent an escalation in confrontation between the West and Russia over disputed sea lanes.
Russia's foreign ministry called the passage of the British warship through the area an act of "blatant provocation" and said it would summon the British ambassador over the incident.
Why was the warship there?
The latest flare-up comes amid months of tensions between Moscow and the West following a build-up earlier this year of Russian forces on the border with Ukraine.
The Kremlin – which annexed Crimea in 2014 – has been riled by the movement of Nato warships in the Black Sea seen as offering support to Ukraine.
HMS Defender is part of the UK Carrier Strike Group currently heading to the Indo-Pacific region.
However, it was announced earlier this month that it would be temporarily breaking away from the group to carry out its “own set of missions” in the Black Sea.
HMS Destroyer arrived in Ukraine as a part of bilateral cooperation between the two countries and an agreement was signed for Britain to help upgrade Ukraine's navy.
Hours before the incident, Russia's embassy in Washington had called on the United States and allies to cancel them.
The UK has said the presence of HMS Defender is part of an operation that demonstrates the country's commitment to maintaining a regular Royal Navy presence in the Western Balkans.
The exercises, it said, are designed to underline allies' commitment to preserving the freedom of navigation and reassure Ukraine, Georgia and Romania of its support in the region.
Russia vs the West
Relations continued to decline following Russia's annexation of Crimea, with further incidents including its intervention in Syria 2015 and its alleged meddling in the 2016 and 2020 U.S. elections.
Last week, Russia's president Vladimir Putin hit out at Nato, describing it as a "relic of the Cold War".
"Nato... is something that was born in the Cold War area," he said. "I'm not sure why it still continues to exist.
"There was a time and there was some talk that this organisation would be transformed. Now it has been kind of forgotten.
"We presume that it is a military organisation. It is an ally of the United States.
"Every once in a while, it makes sense to meet up with your allies, although I can have an idea of how the discussion goes on there."
In a meeting with Putin on 17 June, US president Joe Biden cast Russia as a bit player in a world where Washington is increasingly preoccupied by China.
Aides said Biden wanted to send a message that Putin was isolating himself on the international stage with actions ranging from election interference and cyberattacks on Western nations to his treatment of domestic critics.
Speaking after the meeting, Biden said Russia wants "desperately to remain a major power".
"Russia is in a very, very difficult spot right now," he said. "They are being squeezed by China."
Watch: Biden: Putin doesn't want another 'Cold War'