President Putin has warned he could hit back against countries supplying weapons being used against targets in Russia.
He appeared to be referring to the US and UK, who this week gave Ukraine permission to use long-range missiles over the border.
The Russian president said his military would “respond resolutely in a mirror way” to an “escalation of aggressive actions”.
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“We believe that we have the right to use our weapons against military facilities of the countries that allow to use their weapons against our facilities,” Mr Putin said in a TV address.
British-supplied Storm Shadow missiles were fired into Russia for the first time this week, just days after President Biden authorised the same policy shift.
President Putin responded on Thursday by saying his military had tested a new intermediate-range missile in a strike on the Ukrainian city of Dnipro.
The Russian leader called it the Oreshnik, Russian for hazelnut tree, and said air defences wouldn’t be able to destroy it as it travels 10 times the speed of sound.
Ukraine said earlier that a long-range intercontinental ballistic missile (ICBM) might have been used on Dnipro, but the Pentagon said it believed it was an experimental medium-range weapon.
It said Russia had given notice of the launch through nuclear risk reduction channels.
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Putin fires ‘new type of missile’
Volodymyr Zelenskyy, Ukraine’s president, said on Thursday night that the use of a new missile was a “clear and severe escalation”.
He called it the second serious escalation this year following North Korean troops being sent to bolster Russian forces.
Mr Zelenskyy urged a stronger response from allies and said on X that the Russian leader was “spitting in the face of those in the world who genuinely want peace to be restored”.
Military experts say modern ICBMs and intermediate-range ballistic missiles (IRBMs) are extremely difficult to intercept.
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‘The UK is now directly involved in this war’
Meanwhile, Russia’s ambassador told Sky News that Britain’s missile decision had significantly changed its participation in the conflict.
Andrei Kelin said: “Absolutely, Britain and the UK is now directly involved in this war, because this firing cannot happen without NATO staff, British staff as well.”
He called it a “deliberate cheating of us” and said he had received multiple assurances the Storm Shadows would only be used inside Ukrainian territory.
However, Russia has long used Iranian-made drones to attack Ukrainian cities.
The ambassador said the US and UK move “seriously escalates the situation” and the West should carefully consider Russia’s new rules for using nuclear weapons – as underestimating the risk of escalation is “dangerous”.
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Why is there talk of World War Three?
President Putin again raised the spectre of nuclear weapons this week – something he has done multiple times in recent years – when he approved changes that lower the threshold for such a strike.
Many have dismissed the move as empty sabre rattling, but Russia’s ambassador told Sky News he hoped the change “would be carefully considered by Western experts”.
Russia’s defence ministry also claimed on Thursday to have shot down two British-made Storm Shadow missiles, six HIMARS rockets, and 67 drones.
Experts believe the use of Western missiles inside Russia is unlikely to change the course of the war but could put Russian forces in a more vulnerable position and complicate logistics.