A former Thai Navy diver who had volunteered to help rescue 12 boys and their coach from a cave in northern Thailand has died, according to government officials.

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Former Sgt. Samarn Unan, an ex-SEAL, died at 2:00 a.m. Friday local time (2 p.m. Thursday ET) due to a lack of air while attempting to return to a command center deep underground, Deputy Governor Passakorn Boonyalak said.

The command center is located two kilometers (1.2 miles) inside the cave, where the young soccer team and their coach have been trapped for almost two weeks.

Unan, who was in his mid-30s, was returning from delivering oxygen tanks to the cavern where the boys were when he ran out of air while underwater.

“Diving is always full of risks,” Navy SEAL chief Rear Adm. Aphakorn Yookongkaew said. “He may have passed out,” causing him to drown, “but we have to wait for the autopsy,” he added.

A military aircraft will carry Unan’s body from Chiang Rai to Satthahip Navy Base this evening.

International operation

A huge operation is underway at the Tham Luang Nang Non cave complex, where dozens of Thai Navy SEALs and international experts are attempting to find a way to get the boys out.

The members of the Wild Boar soccer team were reported missing on June 23 when they didn’t return from an outing after soccer practice. They entered the cave during fine weather but became trapped when a sudden downpour flooded the narrow tunnels.

The 12 boys and their coach were found deep inside the cave by two British cave divers on Monday, perched on a rock slab above flood waters, after nine days without food or fresh water.

Since then, rescuers have been examining ways to bring the boys out, including fitting them with full-face oxygen masks and accompanying them on a long, dangerous swim through the tunnels.

However, the death of an experienced diver in the cave system underlines the inherent risks in attempting to move the boys, who are physically weak after days without food.

It takes even the most experienced divers up to five hours to swim through jagged, narrow channels from where the boys are to safety outside.

Speaking to CNN Wednesday, Cade Courtley, a former US Navy SEAL said bringing the children out through the flooded tunnels could be treacherous.

He says that even divers with considerable expertise have been “climbing up, climbing through, going (through water with) zero visibility to finally get through the team.

“Now you’re going to ask 11 to (16) year olds — some of whom can not swim — to make that same journey for the first time breathing air underwater?

“I think that’s a terrible mistake given some of the options we have.”