CHANG RAI, Thailand -- Officials say the massive operation to rescue the soccer team stranded in a flooded cave could begin soon -- if the torrential rains hold off. And inside the cave another problem: Oxygen is running out.

Thai officials appear close to launching their rescue mission, even though the young boys, ages 11 to 16, are weak from being stranded in the cave and are still learning to use the dive equipment they may need to escape the flooded cavern.

Narongsak Osottanakorn, the head of the rescue mission, says they will they will do everything they can to minimize the risk to the boys' lives.

They have furiously pumped water from the cave to lower the water level so the boys can escape without having to swim underwater. That dangerous journey killed a trained Navy SEAL Friday who passed out underwater while delivering oxygen tanks inside the cave.

Those tanks are needed because oxygen levels are dropping, down to an alarming 15 percent. Crews are installing a three-mile-long oxygen tube and have delivered more tanks to the boys' location. They are also considering drilling a hole in the mountain to reach them if a water escape is too dangerous.

Meanwhile, the 25-year old soccer coach who took the boys into the cave has issued an apology to their parents and the trapped children have written letters to their families, delivered out of the cave by divers. In them, they write "I love you, Mom and Dad…Don't worry, we are safe now"; "When I come out, we will go eat fried chicken"; "I miss everybody"; "Don't forget to arrange a birthday party for me."

Fifteen-year-old Kongphob is on the same soccer team as the trapped boys.

He said he is "worried" about his teammates inside the cave. "I don't think they can use diving equipment."

Here at the cave site, there are signs they are preparing for what could be a rescue attempt. They've cleared the street that leads up to the cave, and put up a big green sign that warns about explosions and oxygen tanks. We don't know for sure what they are going to do but they are clearly going to do something.