All five U.S. Marines onboard a military aircraft that crashed in Southern California on Wednesday were killed, U.S. Marine Corps officials confirmed Thursday.

The five Marines, part of Marine Aircraft Group 39, 3rd Marine Aircraft Wing, were on a training mission aboard the MV-22B Osprey when the crash occurred near Glamis, First Lieutenant Duane Kampa said in a statement. Glamis is located just a few miles north of the U.S.-Mexico border and west of the California-Arizona border.

"We mourn the loss of our Marines in this tragic mishap. Our hearts go out to their families and friends as they cope with this tragedy," Maj. Gen. Bradford J. Gering, commanding general of 3rd Marine Aircraft Wing, said in a written statement.

As a matter of policy, the military was not immediately releasing the identities of the Marines killed until 24 hours after notifying next-of-kin.

US NAVY IDENTIFIES PILOT KILLED IN CRASH DURING TRAINING MISSION IN CALIFORNIA

No additional information about was caused the crash was immediately available.

An MV-22B Osprey tiltrotor aircraft attached to the 24th Marine Expeditionary Unit (MEU) prepares to land in support of a theater amphibious combat rehearsal (TACR) at Camp Titin, Jordan. An MV-22B Osprey crashed Wednesday in California, killing all five Marines onboard, the Marine Corps said Thursday. ( Marine Corps 1st Lt. Mark Andries)

Officials have begun equipment recovery efforts and an investigation is underway.

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The crash was the second naval aviation crash in California since Friday when a Super Hornet went down near Death Valley, killing the pilot.

Fox News’ Liz Friden, Louis Casiano and Lucas Tomlinson contributed to this report.

5 US Marines confirmed dead after military aircraft crashes in California

Marines were aboard MV-22B Osprey when aircraft crashed near Glamis, California, on Wednesday