The Pentagon has 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 on Tuesday to deliver the jets to the US Ramstein Air Base in Germany raised the concerning prospect of jets departing from a US 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." 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 US 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 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 MiG-29s and in turn receive American F-16s. Ukrainian pilots are trained to fly the Soviet-era fighter jets. Poland's 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 among former Soviet-bloc NATO members to follow suit. Poland's decision came before Vice-President Kamala Harris was scheduled to depart for Warsaw. The disconnect is likely to cast an awkward layer to the planned talks, which are expected to focus on US efforts to help Poland and other eastern European nations that have taken in two million refugees since the war started less than two weeks ago. The handover of MiGs would signal Western resolve to do more to deter Russia. Militarily, the small number of aircraft, which are inferior to more sophisticated Russian planes, would be unlikely to be a game-changer. Russia has warned that supporting Ukraine's air force would be seen as participating in the conflict and open up suppliers to possible retaliation. 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. Australian Associated Press