Two American soldiers and a U.S. civilian interpreter were killed, and three soldiers injured, in an ambush by a lone ISIS gunman in Palmyra, Syria, during counter-terrorism operations.

The gunman was engaged and killed by U.S. forces, and helicopters evacuated the wounded to a base in Al-Tanf near the Iraq border.

Former President Donald Trump vowed “very serious retaliation” and expressed condolences to the victims and their families.

The attack occurred in a region not fully controlled by the Syrian government and involved a joint patrol with Syrian forces, The Sun has reported.

The incident highlights ongoing U.S.-led efforts against ISIS in Syria, where propaganda and recruitment continue despite prior troop withdrawals.