President Biden has said the US will not give Ukraine any F-16 fighter jets.
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.
Mr Biden responded “no” when asked by a reporter if he would send F-16s to the frontline.
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There are concerns sending such technology could escalate the conflict and be viewed by Russia as NATO countries entering the war by proxy.
However, Britain’s defence secretary said he’s keeping an open mind about joining any future coalition supplying jets.
Ben Wallace told parliament there was a track record of countries saying they would not send arms and then relenting.
France’s President Macron also hasn’t ruled out the possibility but said certain conditions would need to 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.
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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.
However, it’s 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.