Both the UK and US have ruled out sending F-16 fighter jets to Ukraine.
Downing Street said it is “not practical” to send them to Ukraine to bolster its fight against Russia.
While US President Joe Biden responded “no” when asked by a reporter if he would send F-16s to the frontline, and confirmed Washington will not give Kyiv any of the jets.
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It comes after Ukrainian officials stepped up calls for allies to donate advanced warplanes so they can control their airspace.
They are currently using old Soviet-era jets.
There are concerns sending such technology could escalate the conflict and be viewed by Russia as NATO countries entering the war by proxy.
Speaking on Tuesday, the prime minister’s official spokesman said: “The UK’s Typhoon and F-35 fighter jets are extremely sophisticated and take months to learn how to fly. Given that, we believe it is not practical to send those jets into Ukraine.
“We will continue to provide and accelerate our military support to Ukraine and listen carefully to their requests.
“It is the length of time it takes to learn how to use what are very complex pieces of equipment that is the limiting factor in this case but we will explore what more we can do to support Ukraine.”
On Monday, Britain’s defence secretary had said he was keeping an open mind about joining any future coalition supplying jets.
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Ben Wallace told parliament there was a track record of countries saying they would not send arms and then relenting.
France’s President Emmanuel Macron has not ruled out the possibility either but said certain conditions would need to be met.
Ukraine’s defence minister is likely to press his argument for jets when he visits France this week.
There have also been “positive signals” from Poland, according to Ukraine‘s most senior presidential adviser.
The renewed call for jets follows Western allies last week agreeing to donate dozens of tanks to the war.
America and Germany said they would together hand over more than 40, adding to the 14 promised by the UK and the 74 pledged by Poland.
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However, it is believed it could be several months before some of them are delivered and are able to enter battle.
Billions of pounds of weaponry and small arms have already been donated to the country, but Ukraine has said modern tanks are vital to push back Russia and reclaim territory.