Russia has reacted with fury after UK defence secretary Michael Fallon warned there was a “real and present danger” that Moscow could repeat the tactics used to de-stabilise Ukraine against the Baltic States.
Mr Fallon went to describe Russian president Vladimir Putin as posing as great a danger to Europe as Islamic State.
Deputy foreign minister Aleksandr Lukashevich said his words were “beyond diplomatic ethics” and warned that the Kremlin would “find a way to react”.
The furious diplomatic row erupted as the Ministry of Defence disclosed that RAF fighters had again scrambled to intercept long-range Russian bombers off the south coast of England.
PM David Cameron said Moscow appeared to by trying to make “some sort of a point” and that the RAF response showed the UK was well-prepared to react to any Russian incursion.
In his comments to journalists travelling with him to Sierra Leone, Mr Fallon compared the threat from Russian President Vladimir Putin to Islamic State and warned Nato had to be ready to respond to any further aggression “whatever form it takes”.
In a statement reported by the Russia Today website, Mr Lukashevich said his remarks were “absolutely unacceptable”.
“His absolutely unacceptable characteristics of the Russian Federation remind me of last year’s speech of US president Barack Obama before the UN general assembly, in which he mentioned Russia among the three most serious challenges his country was facing,” he said.
“I believe we will find a way to react to Mr Secretary’s statements.”
The MoD said that Typhoon fighter jets from RAF Coningsby in Lincolnshire had intercepted two Bear bombers off the Cornish coast on Wednesday afternoon and escorted them until they left the “UK area of interest”.
“At no time did the Russian military aircraft cross into UK sovereign airspace,” a spokesman said.
Speaking at an event in Felixstowe, Suffolk, Cameron said the incident underlined the readiness of UK forces.
“I think what this episode demonstrates is that we do have the fast jets, the pilots, the systems, in place to protect the United Kingdom,” he said.
“I suspect what’s happening here is that the Russians are trying to make some sort of a point and I don’t think we should dignify it with too much of a response.”
Mr Fallon however warned that tensions with Moscow appeared to be “warming up” in the wake of the Ukraine stand-off.
The latest incursion by Russian aircraft comes after a Russian warship was intercepted by the Royal Navy close to UK waters and two long-range bombers flew down the English Channel off the coast near Bournemouth.
“It is the first time since the height of the Cold War that has happened and it just shows you the need to respond each time he does something like that,” Mr Fallon said.
He expressed concern that the Russian leader could now attempt a repeat of the covert campaign used in the Crimea and eastern Ukraine against the Baltic states of Lithuania, Latvia and Estonia.
“Putin is as great a threat to Europe as Islamic State. We’ve got to be ready for both,” he said.