The first US service members to die in the conflict between the US and Iran were killed by a direct Iranian strike on a makeshift operations center at a civilian port in Kuwait on Sunday morning local time, a source familiar with the situation told CNN.

The death toll from that event at the Shuaiba port has since risen to six, US Central Command announced on Monday afternoon, after the remains of two additional service members were recovered.

Earlier Monday, Defense Secretary Pete Hegseth said that the strike that killed the service members hit a “tactical operation center that was fortified,” but there was “one” projectile that made it through air defenses. CNN previously reported the event was a suspected drone strike.