Rep. Ted Lieu (D-Calif.) is warning the Obama administration that U.S. military personnel could be prosecuted for war crimes for their role in the Saudi Arabia-led coalition bombings of Yemen.

In a letter (pdf) sent Thursday to Secretary of State John Kerry and Defense Secretary Ash Carter, Lieu said American assistance in mid-air refueling and other military support has enabled the coalition to bomb hospitals, schools, and civilian populations amid the fight against the Houthi rebels.

Promising to take precautions does not preclude the U.S. from being complicit in war crimes, the congressman and former Air Force Reserve colonel said.

“I find it deeply troubling that the U.S. apparently has no advanced knowledge of what targets will be struck by jets that are refueled by U.S. personnel with U.S. tankers. Reports last month revealed that State Department lawyers were concerned about potential violations of the Law of Armed Conflict (LOAC) by the coalition, but the administration nevertheless chose to proceed to aid and abet the coalition,” Lieu wrote.

The letter came in response to a statement by a senior official on Wednesday that U.S. support for the coalition does not include “target selection and review.”

Since the start of the war in 2015, the U.S.-backed coalition has killed about 10,000 people, nearly 4,000 of them civilians. That includes at least 150 people killed when an airstrike hit a funeral hall in the capital city of Sana’a last month, which prompted the U.S. to launch a “review” of its support for Saudi Arabia. One specialist later admitted that weak intelligence had caused confusion about who was on the ground that day.

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