Three drones that were being used as suicide bombers on Friday morning struck a U.S. base in Syria.

Two Syrian fighters were hurt in the incident.

The soldiers at the al-Tanf Garrison were able to shoot down two of the drones, but one managed to successfully hit the compound, according to a statement from U.S. Central Command (CENTCOM).

No American troops were injured in the attack.

The two fighters injured were members of a U.S. partner force, the Syrian Free Army, according to CENTCOM.

Joe Buccino, a CENTCOM spokesperson, said “attacks of this kind are unacceptable.”

“They place our troops and our partners at risk and jeopardize the fight against ISIS,” Buccino said in a statement.

The al-Tanf Garrison is located in Syria near the border with Iraq and Jordan.

U.S. troops have used the base to launch counterterrorism operations against ISIS and train Syrian opposition fighters since 2016.

In August, another drone strike hit the garrison but did not cause any injuries or damage to the outpost.