The US has blocked Ukraine from launching long-range missiles into Russia just days after President Donald Trump suggested it would be "impossible" to win the war without attacking Moscow.
US officials told to the Wall Street Journal that a review mechanism was introduced earlier this year by the Pentagon that made it almost impossible for Ukrainian forces to carry out strikes on targets inside Russia.
The revelation comes just days after Mr Trump posted on his Truth Social platform slamming the former Biden administration for not allowing Kyiv to "fight back".
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Mr Trump posted on his Truth Social platform slamming the former Biden administration for not allowing Kyiv to 'fight back'
|PA
He wrote: “It is very hard, if not impossible, to win a war without attacking an invaders country.
"It’s like a great team in sports that has a fantastic defence, but is not allowed to play offence.
"There is no chance of winning! It is like that with Ukraine and Russia.
“Crooked and grossly incompetent Joe Biden would not let Ukraine FIGHT BACK, only DEFEND. How did that work out?”
The US President then posted a picture of himself prodding Russian President Vladimir Putin in the chest, above an image of Richard Nixon doing the same to former Soviet Union leader, Nikita Khrushchev.
Mr Trump had reportedly asked Ukrainian President Volodymyr Zelensky whether his forces had the capability to hit major Russian cities during a phone call in July.
The US President allegedly asked “Volodymyr, can you hit Moscow?… Can you hit St Petersburg too?”, the Financial Times reported.
It is believed that Mr Zelensky said that he would if he was given suitable weapons from Ukraine's Western allies.
However, as a result of the Pentagon's review mechanism, Ukraine has been unable to carry out strikes deep into Russian territory with Army Tactical Missile Systems (Atacms) or Storm Shadows, supplied by the US and UK respectively.
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It is believed that Mr Zelensky said that he would if he was given suitable weapons from Ukraine's Western allies
| REUTERSUkraine have requested to use the Atacms on at least one occasion but this was denied, two US officials revealed to the Wall Street Journal.
The approval process hands US Defence Secretary Pete Hegseth the ultimate decision-making powers when it comes to Ukraine's use of long-range missiles against Russia.
The review mechanism was introduced when the Trump administration had been attempting to lure Mr Putin into entering peace negotiations.
It was believed that some White House officials expressed concerns that allowing US-made missiles to be used to strike targets deep inside Russia may hamper these efforts.
The approval process hands US Defence Secretary Pete Hegseth the ultimate decision-making powers when it comes to Ukraine's use of long-range missiles
|GETTY
The review procedure was introduced by Elbridge Colby, the Pentagon's undersecretary for policy, who is known for taking a cautious stance to any involvement by the US in the Ukraine war.
Mr Colby has long-feared that significant action by the US could deplete Pentagon resources to the benefit of China.
The Pentagon official told a small group of key allies that the US will not play a leading role in security guarantees in Ukraine when the war is over, according to a Politico report.