WARSAW, Poland — The Pentagon on Tuesday rejected Poland’s offer to give the United States its MiG-29 fighter jets for use by Ukraine, in a rare public display of disharmony by NATO allies seeking to boost Ukrainian fighters while avoiding getting caught up in a wider war with Russia.

Pentagon spokesman John Kirby said Poland’s proposal earlier Tuesday to deliver the jets to the U.S. Ramstein Air Base in Germany raised the concerning prospect of jets departing from a U.S. and NATO base to fly into airspace contested with Russia in the Ukraine war.

“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 in a statement.

“It is simply not clear to us that there is a substantive rationale for it,” he said.

Two Polish Air Force Russian-made MiG-29’s fly above and below two Polish Air Force U.S.-made F-16’s fighter jets during an air show in Poland in 2011. Poland will give all its MiG-29 fighter jets to the U.S., apparently agreeing to an arrangement that would allow them to be used by Ukraine’s military. Alik Keplicz/Associated Press

Any decision to provide the MiGs would be a morale booster for Ukraine as Russian attacks on its cities deepen the humanitarian catastrophe. But it also would raise the risks of a wider war.

One senior U.S. diplomat said Poland’s announcement came as a surprise.

“To my knowledge, it wasn’t pre-consulted with us that they plan to get these planes to us,” said U.S. Undersecretary of State Victoria Nuland, who told lawmakers she learned of the proposal as she was driving to testify about the Ukraine crisis before the Senate Foreign Relations Committee.

Ukraine has been pleading for more warplanes and Washington has been looking at a proposal under which Poland would supply Ukraine with the Mig29s and in turn receive American F-16s to make up for their loss. Ukrainian pilots are trained to fly the Soviet-era fighter jets.

The Polish Foreign Ministry announced the plan in a statement, which said the jets would be delivered to Ramstein free of charge.

“At the same time, Poland requests the United States to provide us with used aircraft with corresponding operational capabilities,” it said.

The Polish government also appealed to other owners of MIG-29 jets to follow suit.

Former Soviet-bloc NATO members Bulgaria and Slovakia also still have Soviet-made fighter jets in their air forces.

Poland’s decision to publicly float its plan came the day before Vice President Kamala Harris was scheduled to depart for Warsaw for talks with Polish officials. The disconnect is likely to cast an awkward layer to the talks, which were expected to focus largely on U.S. efforts to help Poland and other eastern European nations that have taken in some 2 million refugees since the war started less than two weeks ago.

The handover of Poland’s 28 Soviet-made MiG-29s would signal Western resolve to do more to deter Russia. Militarily, it would be unlikely to be a game-changer. The number of aircraft is relatively small. The MiG-29s also are inferior to more sophisticated Russian aircraft and could be easy prey for Russian pilots and Russian missiles.

Russia has warned that supporting Ukraine’s air force would be seen in Moscow as participating in the conflict and open up suppliers to possible retaliation.

It would also weaken Poland’s own air force at a time of heightened danger in Eastern Europe.

A transfer of the MiGs to Ukraine is fraught with complications as neither NATO nor the European Union want to be seen as directly involved in the transaction, which will significantly raise already extreme tensions with Russia. The U.S. has no plan to directly transfer the planes to Ukraine.

In order to maintain the pretense that NATO and the EU are not direct participants in the Ukraine conflict, U.S. and Polish officials have been considering a variety of options. One begins with the “donation” of Poland’s MiGs to the United States, as Poland announced on Tuesday.

Under one scenario that has been floated, Poland would deliver the fighter jets to the U.S. base in Germany, where they would be repainted and flown to a non-NATO, non-European Union country. Ukrainian pilots would then come to fly them to Ukraine, under that proposal.

No country has been publicly identified as a transit point, but Kosovo, a non-aligned country that is very friendly with the United States, has been mentioned as one of several nations that might be willing to serve as a middleman.

Poland had been asking for the U.S. to provide it with F-16 fighter jets to replace the MiGs.

F-16 production is backlogged, however, and the next recipient in line for new deliveries is Taiwan, which is facing renewed threats from China and has strong support from both parties in Congress.

In its statement, the Polish government specifically asked for “used” planes, a distinction that would allow the Biden administration to bypass congressional opposition to making Taiwan wait to receive its F-16s.

Earlier Tuesday, British Defense Secretary Ben Wallace said his country would stand by Poland if it handed over the jets, noting that it could face the “direct consequence” of its decision.

“And so we would protect Poland, we’ll help them with anything that they need,” Wallace said on Sky News.

Polish Prime Minister Mateusz Morawiecki said any decision about delivering offensive weapons must be made unanimously by NATO members.

“This is why we are able to give all of our fleet of jet fighters to Ramstein, but we are not ready to make any moves on our own because … we are not a party to this war,” he said.

Senate Minority Leader Mitch McConnell said Tuesday that he believed the aid that Congress hopes to approve later this week for Ukraine will include loan guarantees to help NATO allies replenish their air forces after giving MiGs to Ukraine

Knickmeyer reported from Washington. AP writer Danica Kirka in London and AP Diplomatic Writer Matthew Lee contributed to this report.