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Ukraine has fired UK-supplied Storm Shadow missiles at targets inside Russia for the first time, the BBC understands.
The war-torn country was previously restricted to using the long-range missiles within its own borders.
Reports of the strikes come after Ukraine was given permission from Washington to fire US-supplied missiles at Russian territory.
The government has refused to comment on the reports for operational reasons, but officials confirmed Defence Secretary John Healey spoke to his Ukrainian counterpart on Tuesday night.
Ministers are likely to exercise caution in their response to the reports due to concerns over Russia’s reaction, as well as to ensure the move is not seen as being led by the UK.
In the Commons earlier, Healey said: “Ukraine’s action on the battlefield speaks for itself.”
Ukraine’s Defence Minister Rustem Umerov has also declined to confirm that his country has used the Storm Shadow missiles within Russian territory, but said it was “using all the means to defend our country”.
Matthew Miller, the US State Department’s spokesman, would also not comment on the use of the UK-supplied missile or whether the US was providing navigational assistance for their use.
When asked by the BBC if Ukraine was consulting with or informing the US about the use of missiles provided by the UK, Mr Miller said he would not “speak publicly to the use of another country’s weapons”.
President Volodymyr Zelensky has repeatedly called on Kyiv’s western allies to authorise the use of long-range missiles against targets inside Russia, saying it is the only way to bring about an end to the war.
Storm Shadow is considered an ideal weapon for penetrating hardened bunkers and ammunition stores, such as those used by Russia in its war against Ukraine.
The US and UK had previously not given permission, with suggestions this was related to not wanting to escalate the war
But at the weekend, US President Joe Biden gave the green light for Ukraine to use the Army Tactical Missile System (Atacms) supplied by the US to strike Russia.
On Sunday Ukraine’s President Volodymyr Zelensky reacted to the news – which came via briefings from US officials – saying “such things are not announced, missiles speak for themselves”.
The Atacms was then used by Ukraine to target the Bryansk region bordering Ukraine on Tuesday.
The US has also approved sending landmines to Ukraine, in an attempt to slow down Russian troops.
Speaking at the G20 summit in Rio de Janeiro on Tuesday, UK Prime Minister Sir Starmer said the UK would “ensure Ukraine has what is needed for as long as needed”.
Storm Shadow is an Anglo-French cruise missile with a maximum range of around 250km (155 miles). The French call it Scalp.
It is launched from aircraft then flies at close to the speed of sound, hugging the terrain, before dropping down and detonating its high explosive warhead.
BBC Verify showed images on Telegram claiming to show fragments of a Storm Shadow missile in Kursk to weapons experts.
Amael Kotlarski, Weapons Team manager at Janes, said: “We can confirm that the large, rectangular piece of debris, featuring a hole in the centre, does indeed match part of the mounting interface of the Storm Shadow / SCALP EG missile.”
Another expert could not reach a judgement based on the images.
