U.S. military advisers in Syria had to call in American airstrikes and artillery support to repel an attack late night by pro-Assad regime forces on a headquarters belonging to U.S.-backed rebels. An estimated 100 pro-regime forces were killed by the strikes, said a U.S. official.
A coalition statement said the attack occurred on a "well-known" headquarters belonging to the U.S.-backed Syrian Democratic Forces (SDF) about eight kilometers east of the deconfliction line along the Euphrates River that is used to separate the U.S. area of operations from that of Russia and the Assad regime.
Obviously the group mentioned are not fighting ISIS, but fighting the Regime. We supported other groups in the past and the outcome wasn't helpful to no one.