CHIANG RAI, Thailand, July 6 (Xinhua) -- Thai authorities said on Friday that a former navy SEAL diver working to rescue 12 boy footballers and their coach trapped in a cave has died from lack of oxygen.

SEAL commander Arpakorn Yookongkaew told a news briefing that the rescuer was sending oxygen cylinders inside the cave before he was found unconscious. He was then moved to Chamber 3, a command center set inside the cave and found dead early Friday.

He died due to lack of oxygen when attempting to return to a command center.

The man is a retired Navy Petty Officer 1st Class who volunteered to join the operation, according to reports.