A former Thai navy diver has died while taking part in efforts to rescue 12 boys and their football coach trapped in a flooded cave in Thailand.
Petty Officer Saman Gunan lost consciousness on his way out of the Tham Luang cave complex, where he had been delivering air tanks.
"His job was to deliver oxygen. He did not have enough on his way back," the Chiang Rai deputy governor said.
PO Saman was brought out by his dive partner but could not be revived.
The oxygen level in the chamber where the boys have taken refuge has fallen to 15%, officials said at a news conference. The usual level is about 21%.
The boys and their coach ventured into the cave while it was dry, but were trapped by a sudden deluge of rainfall. Ten days later British rescue divers found them perched on a rock shelf about 4km (2.5 miles) from the cave mouth.
A death in the cave
PO Saman, who was reportedly 38, had left the navy but returned to aid in the rescue operation. Officials said his funeral would be sponsored by the Thai king.
Said to be an avid runner and cyclist, he was part of the massive rescue operation launched after the group became stranded in the Tham Luang cave.
"Inside the cave is tough," said Thai Seal commander Rear Adm Arpakorn Yookongkaew.
"On the way back from setting up oxygen bottles, Petty Officer First Class Saman Gunan passed out. His buddy tried to give him first aid, but he did not respond. We brought him to chamber three and gave him another round of first aid, but he remained unconscious."
The search operation would go on, he said. "I can guarantee that we will not panic, we will not stop our mission, we will not let the sacrifice of our friend go to waste."
Around 1,000 people are involved in the rescue operation, including navy divers, military personnel and civilian volunteers.