U.S. forces conducted a raid against ISIS militants in northwest Syria on Sunday, according to a U.S. official.

Three were killed in the operation, and the U.S. is assessing their identities. There were no U.S. casualties, according to the official.

Earlier this month, U.S. forces killed an "ISIS senior leader" in a strike in northwest Syria, U.S. Central Command (CENTCOM) had announced.

The military identified the leader as Khalid 'Aydd Ahmad Al-Jabouri, who it said was responsible for planning attacks in Europe and Turkey, and developing ISIS's leadership network.

"The death of Khalid 'Aydd Ahmad al-Jabouri will temporarily disrupt the organization's ability to plot external attacks," a release from CENTCOM said at the time.

The U.S. has roughly 900 troops in Syria as part of its effort to defeat ISIS in the region. In recent years, American forces have killed or captured several ISIS leaders in the country.

This is a developing story. Please check back for updates.