Story highlights Marine Cpl. Jordan L. Spears, 21, went missing on Wednesday

"So there's no question" Marine's death related to ISIS operations, Kirby says

Spears has been declared dead by the Navy after rescue efforts failed

His death has not yet been classified, Kirby says

A Marine lost at sea after bailing out of a MV-22 Osprey when it appeared it might crash in the Persian Gulf is believed to be the first American military casualty in support of U.S. operations against ISIS in Iraq and Syria.

Cpl. Jordan L. Spears, 21, was declared dead after search and rescue efforts to locate him were unsuccessful, U.S. Naval Forces Central Command said in a statement released Saturday.

Asked how Spears death will be classified, Pentagon spokesman Navy Rear Adm. John Kirby told reporters the question was still being decided.

Marine Cpl. Jordan L. Spears

"Clearly, that squadron and that ship were in the Gulf, supporting Central Command operations. Some of those operations included operations in Iraq and Syria, at least tangentially, through at least some tangential way, support to those missions," Kirby said, according to a transcript

"So there's no question that -- that this Marine's death is related to the operations that are going on, in some form or fashion."

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Even so, he said he did not know whether the Marine's death would be formally classified as such. The branch of service typically determines how a service member's death is classified.

The military has not detailed the Osprey's mission at the time of the incident, which remains under investigation.

The Osprey, a tilt-rotor aircraft, was deployed as part of the Makin Island Amphibious Ready Group "supporting operations in Iraq and Syria and throughout the region," the statement said.

Spears, a crew chief, went missing Wednesday when the Osprey lost power shortly after takeoff from the USS Makin Island and dropped toward the water, according to the Navy.

Spears and another crew member went into the water when it appeared the Osprey was about to crash, the Navy said.

The pilots managed to get control of the Osprey and land it safely, according to the statement.

Search and rescue crews found one crew member in the water, but were unable to locate Spears of Memphis, Indiana, it said.

"U.S. forces in the North Persian Gulf suspended a search and rescue operation for Spears Oct. 2, after efforts to locate him were unsuccessful," according to the statement.

Spears was assigned to Marine Tiltrotor Squadron 163, Aircraft Group 16, 3rd Aircraft Wing with the 1st Marine Expeditionary Force at Marine Corps Air Station Miramar, California.