A U.S. military service member and three defense contractors perished in a surveillance plane crash in the Philippines on Thursday, according to officials.

U.S. Indo-Pacific Command stated that the Department of Defense-contracted aircraft crashed in Maguindanao del Sur province during a routine intelligence, surveillance, and reconnaissance mission supporting U.S.-Philippine security cooperation.

“The incident occurred during a routine mission in support of U.S.-Philippine security cooperation activities,” the command said in a statement. “We can confirm no survivors of the crash. There were four personnel on board, including one U.S. military service member and three defense contractors,” it added.

A senior U.S. defense official identified the aircraft as a U.S. Marine Corps Beechcraft King Air 350.

The cause of the crash is under investigation. The identities of the victims are being withheld pending notification of next of kin.

Windy Beaty, a provincial disaster-mitigation officer, reported to the Associated Press that witnesses saw smoke and heard an explosion before the plane crashed about half a mile from homes.

Local officials also reported that a water buffalo was killed in the crash.

U.S. forces have a long-standing presence in a Philippine military camp in the south, providing training and advising Filipino forces combating Muslim militants, the AP reported.

The region is home to the nation’s Muslim minority population within a predominantly Roman Catholic country.

‘ Jennifer Griffin and