Even as the Donald Trump administration has taken a mostly hands-off approach to the surge in fighting in Idlib, one of Syria’s last remaining opposition holdouts against the Bashar al-Assad regime, Congress is pushing the State Department to get tougher on reported war crimes in the contested province.

In a letter Tuesday to Secretary of State Mike Pompeo and the US ambassador to the United Nations, Kelly Craft, Reps. Tom Malinowski, D-N.J., and Adam Kinzinger, D-Ill., both of the House Foreign Affairs Committee, and 19 other members of Congress urged the administration to call out three pro-regime strikes in Idlib in July and August that the UN says killed at least 17 civilians and injured 54.

“The deliberate attacks on civilians, protected objects, and medical personnel, as well as the forced displacement of civilians, are war crimes and constitute crimes against humanity,” Malinowski and Kinzinger wrote Tuesday in the letter, which was seen by Al-Monitor. “If the current escalation by government-aligned forces is not slowed, the United Nations assesses that the suffering in Idlib province will likely devolve into the worst humanitarian disaster of the 21st century.”

The members also urged the United States to support investigations into the pro-Assad Tiger Forces, a Russia-backed air intelligence unit that experts have called among the largest fighting organizations in Syria. American officials believe Iranian proxies have increasingly backfilled Assad’s weakened military as it has advanced into Idlib.