(NewsNation) — Ukrainian President Volodymyr Zelenskyy has asked for a no-fly zone to be established over his country to keep Russian planes from bombing. Failing that, he’d like fighter jets so that his country can fight the battle.

That request is under serious consideration, but there are logistical hurdles to overcome along the way. Poland is set to send jets across the border, with a promise from the U.S. to backfill the country’s supplies of jets to make up for the ones it sends.

U.S. Secretary of State Antony Blinken, speaking this weekend about the request, said, “We’re looking actively now at the question of airplanes that Poland may provide to Ukraine and looking how we might be able to backfill should Poland decide to supply those planes.”

Zelenskyy has appealed to U.S. senators for more lethal military aid, asking that his country be given the weapons it needs to defend itself from the Russian assault. In a letter to President Joe Biden, Sens. Rob Portman of Ohio and Jeanne Shaheen from New Hampshire urged the White House to expedite the transfer of American-made F-16s to Poland should it give its Soviet-era Migs to Ukraine.

A production backlog means Poland would essentially be accepting an IOU from the U.S. for the F-16s. The next shipment of F-16s is set to go to Taiwan, a deal Congress would be reluctant to delay with its eyes on any future threat from China.

In addition to Stinger anti-aircraft missiles and other military hardware, the U.S. has already sent $240 million of the promised $350 million in aid, along with a billion dollars in security assistance over the past year.