On Thursday, the Pentagon confirmed the letter’s contents to The Atlantic. “Although DoD has received some reimbursement for inflight refueling assistance provided to the Saudi-led coalition (SLC), U.S. Central Command recently reviewed its records and found errors in accounting where DoD failed to charge the SLC adequately for fuel and refueling services,” Commander Rebecca Rebarich, a Pentagon spokeswoman, told The Atlantic.

The Pentagon’s letter says that it reached these conclusions after Senator Jack Reed, the top Democrat on the Senate Armed Services Committee, made a specific request for information.

Reed, along with seven other Democratic senators, raised the question of reimbursements in a letter to Defense Secretary Jim Mattis in March. The Pentagon’s response admitting “errors in accounting” arrived the day before a key Senate procedural vote on withdrawing U.S. support for the war effort.

“It is clear that the Department has not lived up to its obligation to keep Congress appropriately informed or its responsibility to secure timely reimbursement,” Reed told The Atlantic. “U.S.-provided aerial refueling assistance was provided to the Saudi-led coalition for more than 3.5 years, activities that likely cost tens of millions of dollars. We must ensure that U.S. taxpayers are fully reimbursed for that support.”

When asked by The Atlantic how much reimbursement DoD had received from the Saudi-led coalition, Rebarich said that “CENTCOM is still working through the calculation.” The Saudi and UAE embassies in Washington had not responded to The Atlantic’s requests for comment about any reimbursements at the time of publication.

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Jeffrey Prescott, who served as senior director for Iran, Iraq, Syria, and the Gulf States on the National Security Council in Barack Obama’s administration and is now a strategic consultant to the Penn Biden Center, told The Atlantic: “This is a striking revelation. President Trump has been exceedingly transactional, even seeming to threaten to cast aside NATO if our closest allies didn’t increase their contributions. That is why it is jarring to see that the Trump administration—save for congressional and public pressure—would continue to refuel Saudi and Emirati aircraft without adequate, if any, reimbursement.”

The U.S. refueling of Saudi-led coalition aircraft has long been a source of confusion, because the military has offered differing statements about how much fuel it has provided to its coalition partners. Hill staffers have spent years trying to pin down details of the arrangements, which are carried out via “acquisition and cross-servicing agreements,” or ACSAs, essentially bilateral treaties between the United States and a partner country that allow for the provision of military and logistical support. In the November 27 letter, the Pentagon admitted that the U.S. military refueled Saudi Arabia’s aircraft for at least the first year of the war without any ACSA with the Kingdom.