The U.S. on Saturday announced it conducted a lethal strike in Syria on an al Qaeda affiliate leader it says had direct ties to an ISIS attacker who killed three Americans in early December.

In the space of two days, the Syrian military, aided by tribal militia, has driven Kurdish forces from wide swathes of northern Syria that they have held for more than a decade.

Syria's government and the SDF engaged in months of talks last year to bring Kurdish-run military and civilian bodies under ...