A British spy plane was intercepted mid-air as the jet sped towards annexed Crimea, Russia has claimed.
According to the Moscow defence ministry, an RC-135 reconnaissance aircraft "tried to approach the state border of the Russian Federation in southwestern part of the Crimean Peninsula".
The Ministry of Defence has said it "does not recognise these claims," and that it only flies "in full compliance with international laws."
The war of words comes as The Kremlin warned of “risks of a clash”.
Major General Igor Konashenkov, spokesman for the ministry, claimed an Su-30 fighter was scrambled to intercept the RAF Boeing aircraft before the British aircraft fled.
“About 30 kilometres (19 miles) from the Russian Federation state border, the Su-30 approached the reconnaissance aircraft, after which the British plane changed course away from the Russian border.”
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Footage purportedly showed the incident over the Black Sea south of the Crimea peninsula, annexed by Vladimir Putin in 2014.
"The Russian Defence Ministry records an increase in the military activity of the United States and its NATO allies in the Black Sea region," it said in a statement.
The ministry described the unscheduled drills as "aggressive US actions posing a threat to regional security and strategic stability.”
In 24 hours, four NATO reconnaissance planes were detected and escorted by the Russian anti-aircraft missile forces, the ministry has claimed.
The West insists that under international law Crimea belongs to Ukraine.
Earlier the Kremlin had warned that the West was “playing with fire” by deploying warships in the Black Sea, as Russia warned of the “risks of a clash”.
Putin is worried about swelling soldier numbers on both sides of the Polish-Belarus border, but naval threats in the Black Sea was “absolutely the subject of his concern, and he talked about it,” said Dmitry Peskov, Putin's spokesman.
And it's not just Putin that's worried, as Russian deputy foreign ministry Sergei Ryabkov hit out: "What are American ships doing in the Black Sea thousands of miles from their permanent bases?
“No explanations of it being all about freedom of navigation work. All this is playing with fire, it is yet another attempt to test us.”
Putin has separately ordered his military and industrial chiefs to speed up the modernisation of weapons.
He ordered arms-makers: "We need to focus on introducing advanced information, bio- and cognitive technology, (and) hypersonic arms.”
He also called for “weapons based on new physical principles, as well as cutting-edge reconnaissance, navigation, communications and control systems.”
The full statement given to The Mirror from the MoD stated: “We do not recognise these claims.
“Wherever the RAF operates, it does so in full compliance with international laws and exercises its right to freedom of overflight.”
