The diver was about half a mile from where the 12 young soccer players and their coach have been trapped since June 23, when rains flooded the vast and complex cave system they were exploring in northern Thailand.
Some Thai officials have proposed leaving the boys and their coach in the cave for four months, until the water subsides and they can walk out.
At a late night press conference, Chiang Rai province governor Narongsak Osottanakorn said there was "a plan in place".
Retired Petty Officer Saman Gunan was delivering air tanks to the stranded group, who are in a subterranean chamber with oxygen levels running low, the BBC reported.
The huge operation to rescue the group involves scores of Thai Navy SEALs, in addition to experts and volunteer divers from parts of Europe and Asia, as well as Australia and the US.
A diver who spent time with the boys said earlier the youngsters wanted to know the results of the matches.
The boys, 11 to 16, and their 25-year-old coach went exploring in the cave after a soccer game, when monsoon flooding cut off their escape and prevented rescuers from finding them for nearly 10 days. "I promise to take the very best care of the kids", he said.
"Thank you all for the support", the coach wrote.
"Don't worry, we are all strong", one child said in a note. "Don't forget to throw my birthday party!" "Tell Yord, prepare to bring me fried chicken to eat".
Other messages written on pages from a notebook saw the boys send messages of reassurance to their anxious relatives.
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However the 30-year-old could still play a part as he returned to training ahead of Monday's last 16 clash. The important thing is that there is no injury. " Marcelo was a muscle spasm in the area of the spine".
The rest of the scribbled letters on pages from a notebook struck similar messages for parents and urged them not to worry.
"Don't worry about me. I love you, mum, dad and brother", Nick wrote.
A former Thai Navy diver died on Thursday night while trying to help rescue the 12 boys.
Rescuers found them 10 days later and are now working to find a way to get them out.
The players were also able to write messages to their families in the same notebook that Chanthawong issued his apology.
"I confirm that we are at war with water and time from the first day up to today", said Narongsak.
Saman Kunan was returning from an overnight mission placing oxygen canisters when he lost consciousness and died Friday morning, Thai navy SEAL commander Arpakorn Yookongkaew told reporters Friday.
The boys, aged between 11 and 16 and not all of whom are capable swimmers, are hurriedly being taught to take on a treacherous dive through narrow, muddy, submerged passageways. He said the boys were still healthy and have practiced wearing diving masks and breathing in preparation for the diving possibility.
So far, around 1,000 people have got involved in the rescue operations..
The boys are being trained in the basics of diving in case the flood waters force authorities into a sudden evacuation through twisting and jagged passageways.
"If, as we all hope, they are reunited with their families in the coming days and their health allows them to travel, Federation Internationale de Football Association would be delighted to invite them to attend the 2018 World Cup final in Moscow as our guests".