The deal would involve Ukraine receiving Russian-made warplanes from Poland, which would then be given American F-16s by the US to refill its stocks. It comes amid fears Russia will increase aerial attacks given the slow progress of parts of its ground campaign.

The White House said it was negotiating with Poland and consulting other Nato allies but that there were “a number of challenging practical questions, including how the planes could actually be transferred from Poland to Ukraine”.

“We are also working on the capabilities we could provide to backfill Poland if it decided to transfer planes to Ukraine,” a White House spokesperson said.