The reasons listed here:
WASHINGTON – Today, the U.S. Department of the Treasury’s Office of Foreign Assets Control (OFAC) is sanctioning eight Syrian prisons run by the Assad regime’s intelligence apparatus, which have been sites of human rights abuses against political prisoners and other detainees. OFAC is also...
home.treasury.gov
"OFAC is also sanctioning Syrian armed group Ahrar al-Sharqiya, which operates in northern Syria, for abuses against civilians, and is also sanctioning two of the group’s leaders. Ahrar al-Sharqiya has committed numerous crimes against civilians, particularly Syrian Kurds, including unlawful killings, abductions, torture, and seizures of private property. The group has also incorporated former Islamic State of Iraq and Syria (ISIS) members into its ranks. These horrific acts compound the suffering of a population that has repeatedly endured mass displacement."
They also sanctioned Assad intelligence officials.