The Pentagon has slammed the door on any plans to provide MiG fighter jets to Ukraine, even through a second country, calling it a “high-risk” venture that would not significantly change the effectiveness of the Ukrainian Air Force.

Pentagon press secretary John Kirby told reporters that Defence Secretary Lloyd Austin spoke with his Polish counterpart on Wednesday and told him the US assessment.

He said the US is pursuing other options that would provide more critical military needs to Ukraine such as air defence and anti-armour weapons systems.

Poland had said it was prepared to hand over MiG-29 planes to Nato that could then be delivered to Ukraine, but Mr Kirby said US intelligence concluded that it could be considered escalatory and trigger a “significant” Russian reaction.

Mr Kirby’s remarks went beyond his comments in a statement on Tuesday, rejecting Poland’s offer to give fighter jets to the United States for transfer to Ukraine.

He said individual Nato nations can make up their own minds on what assistance to give Ukraine, but it is questionable whether any would provide fighters without US support.