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Poland offered to give its entire fleet of MiG-29 fighter jets to the U.S. in exchange for a chance to buy American F-16s as part of a deal to bolster the Ukrainian air force while upgrading the Poles’ with NATO aircraft.

"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 Tuesday. "At the same time, Poland requests the United States to provide us with used aircraft with corresponding operational capabilities. Poland is ready to immediately establish the conditions of purchase of the planes."

The Poles also requested any other NATO member countries that have MiGs of their own take similar action. Those may include Bulgaria and Slovakia.

Polish Air Force MiG-29

Polish Air Force MiG-29 pilot Adrian Rojek performs during the Radom Air Show at an airport in Radom, Poland August 23, 2015.  (REUTERS/Kacper Pempel)

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Ukrainian defense officials for days have been asking for help with supplies ranging from helmets to ammunition and fighter jets – a request that Poland appeared ready to fulfill almost two weeks into Russia’s invasion of its smaller neighbor.

Undersecretary of State Victoria Nuland said during a Senate Foreign Relations Committee hearing Tuesday that the announcement was "a surprise move by the Poles."

"To my knowledge, it wasn't pre-consulted with us that they planned to give these planes to us," she said. "But as you know, we have been having consultations with them for a couple of days now about this request from the Ukrainians to receive their aircraft, and were they to donate them, whether we would be able to support backfill in their own security needs."

Earlier Tuesday, a bipartisan group of U.S. lawmakers sent a letter to President Biden urging him to support a deal with Poland.

But Pentagon press secretary John Kirby distanced the U.S. from the proposal later in the day, saying that while the decision to hand over jets to Ukraine is in the hands of the Polish government, American involvement "raises serious concerns for the entire NATO alliance."

"It is simply not clear to us that there is substantive rationale for it," he said in a statement. "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." 

He said the U.S. would continue talks with Poland and the rest of NATO regarding the issue.

Ukrainian pilots have been trained on the Soviet-era MiG jets. Poland, which joined NATO in 1999, aimed to replace the donated MiGs with used F-16s.

Poland, which joined NATO in 1999, aims to replace its fleet with used F-16s and train its pilots to fly them.

Poland, which joined NATO in 1999, aims to replace its fleet with used F-16s and train its pilots to fly them. (U.S. Air Force photo by Staff Sgt. Andrew Lee)

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Poland has 28 MiG-29s that it plans to hand over. According to the CIA’s World Factbook, "Ukraine has a broad defense industry capable of…maintaining and upgrading Soviet-era combat aircraft."

Polish Prime Minister Mateusz Morawiecki told reporters in London earlier Tuesday that despite the decision, "neither Poland or NATO are parties" to the war in Ukraine.

Russia meanwhile has warned that it will view support of Ukraine’s air force as an escalation of the conflict and that it may retaliate.

The United Kingdom, which has an advanced air force of its own, said it would support Poland’s move as war rages in Eastern Europe.

Members of the Ukrainian military arrive to reinforce a forward position on the eastern frontline near Kalynivka village on March 08, 2022, in Kyiv, Ukraine.

Members of the Ukrainian military arrive to reinforce a forward position on the eastern frontline near Kalynivka village on March 08, 2022, in Kyiv, Ukraine. (Photo by Chris McGrath/Getty Images)

"We would protect Poland," British Defense Secretary Ben Wallace told the UK’s Sky News Tuesday. "We’ll help them with anything that they need."

President Biden said during his State of the Union address last week that the U.S. and allies would defend "NATO territory with the full force of our collective power – every single inch." 

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Almost two weeks into the invasion, Russia has failed to assert air superiority over Ukraine. Defense forces claim to have shot down 48 Russian aircraft, an additional 80 helicopters and seven UAVs.

Ukraine’s military has released figures detailing its own losses.

Fox News’ David Aaro, Liz Friden and The Associated Press contributed to this report.