Vice President Kamala Harris's trip to Warsaw to thank Poland for hosting hundreds of thousands of Ukrainians fleeing the Russian invasion took an unexpected turn before she left Washington on Wednesday.

On Tuesday, the Polish government came out with a plan to transfer its Russian-made fighter jets to a U.S. military base in Germany, with the expectation that the planes would then be handed over to Ukrainian pilots trying to repel Russian forces. In return, the United States would supply Poland with American-made planes with "equivalent capabilities."

But the Poles did not discuss this idea with the Biden administration before announcing it, and the Pentagon quickly rejected the idea as indefensible. At a time when NATO allies are trying to help Ukraine without becoming involved in a wider war with Russia.

Daniel Fried, who served as U.S. ambassador to Poland under President Bill Clinton and was a senior advisor in the administrations of George W. Bush and Barack Obama, said. "There are many discussions about the way forward that need to be held with the Poles, and it's better to have them in a face-to-face conversation."

Harris is expected to continue talks with the Poles on transferring fighter jets to Ukrainians during her visit to Warsaw, according to a senior administration official, who reviewed the trip on condition of anonymity. The official added that it remains a priority for the Biden administration.

Harris is scheduled to meet Thursday with Polish President Andrzej Sebastian Duda and Prime Minister Mateusz Morawiecki as well as with Ukrainians who fled to Poland. She will also meet Canadian Prime Minister Justin Trudeau while in Warsaw. Trudeau was in Europe this week to meet with Ukraine allies.

Harris will travel on Friday to Bucharest to meet with Romanian President Klaus Iohannis.

The vice president is also expected to use the meetings in Poland and Romania to emphasize the United States' commitment to NATO and the need for continued humanitarian and military aid to Ukraine. She will also highlight the need for allies to continue their close coordination moving forward.

Biden has praised Poland and other Eastern European countries amid what has become a huge and worsening humanitarian crisis. About two million people have fled Ukraine, and more than half of the refugees have gone to Poland.

Biden said Tuesday he is committed to helping Ukraine’s neighbors bear some of the financial burden of assisting refugees. He previously deployed 4,700 additional U.S. troops to Poland to bolster defense of NATO's eastern flank.

Biden added, "I have made it clear that the United States will share in the responsibility of caring for refugees so that the costs don't fall entirely on the European countries neighboring Ukraine." He was looking to Congress to pass a $14 billion aid package to help Ukraine and its allies in Eastern Europe.

Victoria Nuland, Deputy Secretary of State for Political Affairs, told the Senate Foreign Relations Committee that she saw the Polish government's announcement while on her way to Capitol Hill to testify.

Secretary of State Antony Blinken said Sunday the United States is working with Poland on plans to provide Ukraine with fighter jets and "fill" Poland’s needs. However, the Polish government clarified that it will not send its fighter jets directly to Ukraine or allow the use of its airports.

According to a U.S. official familiar with the talks, Poland’s idea of transferring its MiG fighter jets to the U.S. was not raised during discussions with Blinken.

The official, speaking on condition of anonymity to discuss the sensitive matter, said White House officials do not believe the proposal would easily solve the logistical challenges of providing planes to Ukraine and questioned the logic of transferring the aircraft to a major NATO base in Germany only to send them back to Eastern Europe.

Ukrainian President Volodymyr Zelensky called on NATO to impose a no-fly zone over Ukraine or provide Ukraine with fighter jets. NATO rejected the no-fly zone idea, saying such a move would lead to the largest conflict in Europe since World War II and would escalate further.

Texas Rep. Michael McCaul, the top Republican on the House Foreign Affairs Committee, said late Tuesday that he hopes the administration can reach a better deal with Poland. "I hope they can go back to Poland, renegotiate that, and give them assurances that we will deliver" fighter jets, he said.

McCaul also said more lethal drones could be another option to help provide airpower to Ukrainians.

Despite the split over Poland's proposal, the White House remained determined to send Harris to Poland and Romania, where it hopes to highlight efforts to build a united front with European neighbors and Western allies.

Harris traveled to the Munich Security Conference last month to rally European allies in the days before the invasion. She also met with Zelensky and other European officials.

White House press secretary Jen Psaki said, "The vice president’s trip to Poland and Europe is part of our efforts to show our strong support for our NATO allies and partners, the security assistance they provide, and their role in accepting and welcoming refugees from Ukraine."