The Pentagon on Tuesday rejected Poland's surprise announcement that it would give the United States its MiG-29 fighter jets for use by Ukraine, a rare 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 declaration that it intended to deliver the 28 jets to the U.S. Ramstein Air Base in Germany raised the concerning prospect of warplanes departing from a U.S. and NATO base to fly into airspace contested with Russia in the Ukraine conflict.

"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.

The proposed gift of more warplanes would be a morale booster for Ukrainians under pounding Russian assault for nearly two weeks. But it also raises the risk of the war expanding beyond Ukraine.

Russia has declared that supporting Ukraine's air force would be tantamount to joining the war, and could spur retaliation.

White House officials were blindsided by the Polish announcement on the MiGs. The proposal did not come up during talks with Secretary of State Antony Blinken when he was recently in Poland, according to a U.S. official familiar with the talks.

The U.S. official, who spoke on the condition of anonymity, said White House officials did not think the proposal would easily solve the logistical challenges of providing aircraft to Ukraine.

U.S. Undersecretary of State Victoria Nuland told lawmakers at a hearing on the Ukraine crisis Tuesday she learned of Poland's plans only while driving to the hearing.

"To my knowledge, it wasn't pre-consulted with us," Nuland told senators.

Ukraine has been pleading for more warplanes as it resists mightier Russian forces. Washington has been looking at a proposal under which Poland would supply Ukraine with the MiG-29s 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 publicly floated its plan the day before Vice President Kamala Harris is scheduled to depart for Warsaw for talks with Polish officials. The disconnect is likely to add 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.

Additional air-defense capabilities are the No. 1 priority for Ukraine's military right now, the country's defense attache in Washington, Maj. Gen. Borys Kremenetskyi, told The Associated Press on Tuesday after returning from a meeting at the Pentagon. "It can be ground-based air-defense systems. It can be fighter jets, whatever possible," he said.

Ukraine also needs additional anti-tank, anti-armor weapons and coastal defense capabilities to defend against Russian ships in the south, he said.

The handover of Poland's 28 Soviet-made MiG-29s would signal Western resolve to do more for Ukraine. Militarily, however, the number of planes offered would make it unlikely to be a game-changer. And MiG-29s are inferior to more sophisticated Russian aircraft and could be easy prey for Russian pilots and Russian missiles.

A senior U.S. defense official has said Ukrainians are flying relatively few of their existing aircraft, for relatively little time, as it is. The defense official, who spoke on condition of anonymity to discuss the U.S. assessment, said it's possible that Ukraine does not need more planes and would benefit most from more of the weapons it uses effectively every day, including anti-aircraft Stinger and anti-tank Javelin missiles.

The official also said that Russia currently has the capacity to reach almost the entire country of Ukraine with its surface-to-air missiles, including from within Russia and from ships in the Black Sea.

Any MiG transfer is fraught with complications. Neither NATO nor the European Union wants to be seen as directly involved in such a transaction, which would sharply raise already extreme tensions with Russia.

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, 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-EU country. Ukrainian pilots would then come to fly them to Ukraine.

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 middle point.

Poland's proposed gift would also weaken Poland's own air force at a time of heightened danger in eastern Europe.

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.

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.

From The Associated Press