WASHINGTON 

The Pentagon on Tuesday turned down a proposal from Poland to transfer all of its MiG-29 fighter jets to a US airbase in Germany for backing Ukraine amid its war with Russia.

"The prospect of fighter jets 'at the disposal of the Government of the United States of America' departing from a U.S./NATO base in Germany to fly into airspace that is contested with Russia over Ukraine raises serious concerns for the entire NATO alliance," said spokesman John Kirby in a statement.

"It is simply not clear to us that there is a substantive rationale for it."

Kirby said the decision about whether to transfer the Polish-owned jets to Ukraine is "ultimately one for" the Polish government.

He said the US will continue to consult with its allies and partners about the nation's continued security assistance to Ukraine, adding "Poland’s proposal shows just some of the complexities this issue presents.”

"We will continue to consult with Poland and our other NATO allies about this issue and the difficult logistical challenges it presents, but we do not believe Poland’s proposal is a tenable one," Kirby said.

Earlier in the day, Poland expressed its readiness to hand over all of its MIG-29 jets to the US.

“The authorities of the Republic of Poland, after consultations between the President and the Government, are ready to deploy – immediately and free of charge – all their MIG-29 jets to the Ramstein Air Base and place them at the disposal of the Government of the United States of America,” the Polish Foreign Ministry said in a statement.

Calling on other NATO allies that possess MIG-29 jets to "act in the same vein," the country also said it requested the US to provide "used aircraft with corresponding operational capabilities."

"Poland is ready to immediately establish the conditions of purchase of the planes," it added.

*Kasim Ileri contributed to this story