On 13 December, a gunman ambushed a U.S.-Syrian joint patrol near the historic city of Palmyra, killing three U.S. personnel (two soldiers belonging to the Iowa National Guard and one civilian interpreter) and wounding two more as well as two members of the Syrian security services. Syrian forces killed the gunman at the scene.

U.S. Central Command attributed the attack to a “lone ISIS gunman”, while Syrian officials confirmed the assailant belonged to the Syrian security services. Syria’s Interior Ministry shared publicly that an evaluation issued on 10 December had flagged him as potentially holding extremist ideas, and that he did not have a leadership position, but did not offer any insight on the individual’s recruitment history. Unofficial reports identified him as a former rebel fighter from the countryside of the Aleppo governorate. President Trump mourned the losses and vowed “very serious retaliation” for the attack, while Syrian President Ahmed al-Sharaa publicly condemned the attack in an official telegram to Trump, expressing sympathy for the victims and reaffirming Syria’s commitment to counter-terrorism cooperation.

This marks the first fatal attack on U.S. forces in Syria since Assad’s fall one year ago, and the deadliest day for U.S. forces since the January 2019 Manbij bombing that killed four U.S. military personnel. The incident comes just weeks after Syria formally joined the U.S.-led counter-ISIS coalition, becoming the 90th member; President al-Sharaa announced this move during his historic White House visit on 10 November. Joint patrols like the one targeted Saturday, represent one dimension of the military cooperation now under way.

The attack from within Syria’s own ranks underscores one of the state’s critical vulnerabilities. Harming international perceptions of stability and security in Syria, and making Damascus less attractive to international partners, does not require large numbers of troops. One or two individuals with access and know-how can do great harm. Concerningly, the attacker is unlikely to be alone in having these qualities. Because authorities have worked so quickly to consolidate disparate armed factions into state structures, vetting, integration and oversight have been uneven, leaving Syria’s reconstituted security institutions vulnerable to infiltration.

One question now is how much this incident will erode confidence in joint U.S.-Syrian operations and whether this can be mitigated by thoroughly reviewing vetting procedures and cooperation protocols, and taking corrective steps. Among other possible effects, the incident may accelerate discussions around scaling back U.S. troop presence in Syria; constraining counter-ISIS operations as assets are redirected to force protection; and prompting the U.S. to consider greater emphasis on working with the Syrian Democratic Forces in the country’s north east, which has been the U.S.’ local partner for the past decade. 

For Damascus, the 13 December attack compounds pressure on al-Sharaa’s government at a precarious moment, boosting those sceptical that al-Sharaa can successfully assert a monopoly over the use of force in Syria. For now, bridging the gap between its formal membership in the counter-ISIS coalition and providing operational security remains a central challenge for Damascus’s evolving counter-terrorism partnership with Washington and other coalition members.