The U.S. Marines in Okinawa said Tuesday that it has detected “several” cases of COVID-19 infections at the contentious U.S. Marine Corps Air Station Futenma in the prefecture.

“Several SOFA status personnel aboard MCAS Futenma have tested positive for COVID-19,” Marine Corps Installations Pacific said in a statement. “The individuals that have tested positive and their close contacts have been moved into isolation. At this time, the source of exposure is unknown.”

The MCIPAC did not immediately respond to a request for comment on the exact number of cases.