"At first we thought that we could sustain the kids' lives for a long time where they are now, but now, many things have changed".
The letter signed by FIFA President Gianni Infantino also says the organization would like to invite the youngsters and their coach to the World Cup final in Russian Federation, should they be rescued in time and are healthy enough to travel.
Authorities have confirmed the diver's death was caused by lack of oxygen, and he died while making his way out of the cave complex where the group is trapped.
Navy SEAL commander Rear Adm. Arpakorn Yookongkaew separately explained the ethic driving the SEALs' mission and why Saman's death would not deter them from their course. It is tied to a telephone line to provide a channel of communication for the kids, who are stuck deep in the complex but are being looked after by four SEALs, including a medic.
Rescuers said they will not immediately attempt an underwater evacuation because the boys have not yet learned adequate diving skills - but will if heavy rains recommence.
British divers Rick Stanton, a fireman in his fifties from Coventry, and John Volanthen, an IT consultant based in Bristol in his forties, were the first to reach the group. He says weather conditions have been in their favour and water levels have been falling over the last few days.
At this time though, the only way for the boys to get out of the cave is by diving, something cave rescue experts warn is extremely unsafe even for those with experience.
Gunan, 38, formerly served in the Royal Thai Navy's Underwater Demolition Assault Unit, colloquially known as the Thai Navy SEALs.
Attempts to resuscitate him failed.
Thai divers would lead the mission and USA divers would preposition oxygen tanks, the United States official said. "We will stay until the mission is complete", Arpakorn added.
The governor has said the 13 may not be extracted at the same time, depending on their condition.
They have practised wearing diving masks and breathing in preparation for the diving possibility.
On Friday morning forecast downpours held off, giving a glimmer of respite to the rescue workers who are pumping out the water, whilst plotting the complicated extraction plan.
A firefighter who has been working on draining the water said levels in parts of the passage leading to the chamber were still flooded all the way to the ceiling, making diving the only way out. The idea is to get some headroom so the boys would not be reliant on scuba apparatus for a long stretch and could keep their heads above water.
Narongsak said they would have to drill through 600 metres (1,970 feet) of fragile limestone rock to reach the boys and were discussing drilling angles. And without proper oxygen levels, staying put could also prove deadly.
The boys are 11-16 years old and their coach is 25.
One of his enterprises is Boring Co., which digs tunnels for advanced transport systems and has advanced ground-penetrating radar.
Elon Musk, the entrepreneur behind the Tesla automobile and the SpaceX rocket company, said he would send engineers to help.