Elon Musk has disputed reports about the usefulness of his plan to rescue the Thai boys from underground.

The SpaceX boss said he had invented a tiny submarine that could be used to carry the boys out from the cave network, without having to teach them to dive or swim.

Mr Musk's plan was reported to have been called "not practical" by Narongsak Osatanakorn, who has been co-ordinating the mission. That report came after some criticism of the plan from people who argued that the relatively large submarine would not be able to fit around the tight cave network the boys had to navigate.

“Even though their equipment is technologically sophisticated, it doesn’t fit with our mission to go in the cave,” Mr Osatanakorn told the BBC.

Thailand schoolboys rescue - in pictures Show all 21 1 /21 Thailand schoolboys rescue - in pictures Thailand schoolboys rescue - in pictures Police and military personnel use umbrellas to cover a stretcher near a helicopter and an ambulance at a military airport in Chiang Rai as rescue operations continue for those still trapped inside the cave in Khun Nam Nang Non Forest Park in the Mae Sai district. Four boys among the group of 13 trapped in a flooded Thai cave for more than a fortnight were rescued on July 8 after surviving a treacherous escape, raising hopes elite divers would also save the others soon. AFP/Getty Thailand schoolboys rescue - in pictures Thai rescue team members walk inside the cave Rex Features Thailand schoolboys rescue - in pictures An ambulance exits from the Tham Luang cave area AFP/Getty Images Thailand schoolboys rescue - in pictures A military helicopter carrying rescued schoolboys approaches to land at a military airport in Chiang Rai REUTERS Thailand schoolboys rescue - in pictures Rescuers hands locked with a caption reading "We Thai and the international teams join forces to bring the young Wild Boars home" where 12 boys and their soccer coach have been trapped since June 23 in a cave in Mae Sai, Chiang Rai province, northern Thailand. The operation has begun to rescue 12 boys and their soccer coach who will need to dive out of the flooded Thai cave where they have been trapped for more than two weeks, with officials saying Sunday morning that "today is D-Day. AP Thailand schoolboys rescue - in pictures A Thai policeman stands guard at an entrance of the cave as rescue operations continue for 12 boys and their coach trapped at Tham Luang cave at Khun Nam Nang Non Forest Park in the Mae Sai district of Chiang Rai province on early July 8, 2018. Thai authorities told media on July 8 to leave a camp site near the cave where 12 boys and their coach have been trapped for more than two weeks so that "victims" could be helped, possibly signalling a long-awaited rescue effort to get them out. AFP/Getty Images Thailand schoolboys rescue - in pictures Rescuers are seen drillining ahead of the operation at the Tham Luang cave complex, where 12 boys and their soccer coach are trapped, in the northern province of Chiang Rai, Thailand REUTERS Thailand schoolboys rescue - in pictures Rescuers are seen drillining ahead of the operation at the Tham Luang cave complex, where 12 boys and their soccer coach are trapped, in the northern province of Chiang Rai, Thailand REUTERS Thailand schoolboys rescue - in pictures Ruamkatanyu Foundation rescuers are seen drillining ahead of the operation at the Tham Luang cave complex, where 12 boys and their soccer coach are trapped, in the northern province of Chiang Rai, Thailand REUTERS Thailand schoolboys rescue - in pictures Thai policemen stand guard near a cave where 12 boys and their soccer coach have been trapped since June 23, in Mae Sai, Chiang Rai province, in northern Thailand Sunday, July 8, 2018. Thai authorities are racing to pump out water from the flooded cave before more rains are forecast to hit the northern region. AP Thailand schoolboys rescue - in pictures Journalists clear and prepare to leave the cave area during the 'D-Day' for the ongoing rescue operation for the child soccer team and their assistant coach to exit the cave at Tham Luang cave in Khun Nam Nang Non Forest Park, Chiang Rai province, Thailand, 08 July 2018. The officials' operations are underway to safely bring out the 13 members of the youth soccer team including their assistant coach who have been trapped in Tham Luang cave since 23 June 2018, out of the cave according to former Chiang Rai Governor Narongsak Osottanakorn said. EPA Thailand schoolboys rescue - in pictures Thai family members of missing football players and their coach (R) pass to meet with the officers during rescue operations to save a soccer team at Tham Luang cave in Khun Nam Nang Non Forest Park, Chiang Rai province, Thailand, 03 July 2018. According to Chiang Rai provincial Governor Narongsak Osatanakorn rescuers are taking supplies and food into the cave to sustain the team while there extraction is worked out. EPA Thailand schoolboys rescue - in pictures Rescuer walk out from cave where 12 boys and their soccer coach have been trapped since June 23, in Mae Sai, Chiang Rai province, in northern Thailand Sunday, July 8, 2018. Thai authorities are racing to pump out water from the flooded cave before more rains are forecast to hit the northern region. AP Thailand schoolboys rescue - in pictures Policeman line up on the main road leading to Tham Luang Nang Non cave on July 8, 2018 in Chiang Rai, Thailand. Divers began an effort to pull the 12 boys and their soccer coach on Sunday morning after they were found alive in the cave at northern Thailand. Videos released by the Thai Navy SEAL shows the boys, aged 11 to 16, and their 25-year-old coach are in good health in Tham Luang Nang Non cave and the challenge now will be to extract the party safely. Getty Images Thailand schoolboys rescue - in pictures Rescue workers along the main road leading to Tham Luang Nang Non cave as the first 2 ambulances carrying 2 boys pass by on July 8, 2018 in Chiang Rai, Thailand. Divers began an effort to pull the 12 boys and their soccer coach on Sunday morning after they were found alive in the cave at northern Thailand. Videos released by the Thai Navy SEAL shows the boys, aged 11 to 16, and their 25-year-old coach are in good health in Tham Luang Nang Non cave and the challenge now will be to extract the party safely. Getty Images Thailand schoolboys rescue - in pictures Thai medics and police officers evacuate the first two children with a helicopter after rescued from Tham Luang cave before heading to hospital, at a helicopter pad in Chiang Rai province, Thailand, 08 July 2018. Members of a children soccer team and their assistant coach who have been trapped in Tham Luang cave EPA Thailand schoolboys rescue - in pictures An ambulance transporting the children who have been rescued, arrives at hospital in Chiang Rai province, Thailand, 08 July 2018. The first six children have been confirmed to rescue on 08 July 2018 after have been trapped in Tham Luang cave since 23 June 2018. Four members of a children soccer team and their assistant coach who have been trapped in Tham Luang cave since 23 June 2018 have been rescued on 08 July 2018, according to former Chiang Rai Governor Narongsak Osottanakorn said. EPA Thailand schoolboys rescue - in pictures Ambulances transport boys rescued from Tham Luang Nang Non cave to hospital on July 8, 2018 in Chiang Rai, Thailand. Divers began an effort to pull the 12 boys and their soccer coach on Sunday morning after they were found alive in the cave at northern Thailand. Videos released by the Thai Navy SEAL shows the boys, aged 11 to 16, and their 25-year-old coach are in good health in Tham Luang Nang Non cave and the challenge now will be to extract the party safely. Getty Thailand schoolboys rescue - in pictures Medical staff await for the rescued Thai children at Chiang Rai Prachanukroh Hospital in Chiang Rai. The twelve missing Thai children and their adult coach went missing after entering a cave at Tham Luang, in Chian Rai Privince Thailand schoolboys rescue - in pictures Ambulances transporting children after being rescue from Tham Luang cave, arrive Chiangrai Prachanukroh Hospital in Chiang Rai province, Thailand, 08 July 2018. Six children of a child soccer team have been rescued on 08 July 2018 after 12 of them and their assistant coach have been trapped in Tham Luang cave since 23 June 2018. EPA Thailand schoolboys rescue - in pictures Ambulances transporting children after being rescue from Tham Luang cave, arrive Chiangrai Prachanukroh Hospital in Chiang Rai province, Thailand, 08 July 2018. Six children of a child soccer team have been rescued on 08 July 2018 after 12 of them and their assistant coach have been trapped in Tham Luang cave since 23 June 2018. EPA

But Mr Musk said that he was certain the submarine would have been able to navigate the tight gaps and difficult corners inside the cave network.

"Based on extensive cave video review & discussion with several divers who know journey, SpaceX engineering is absolutely certain that mini-sub can do entire journey & demonstrate at any time," he wrote. In response to a question about a particularly difficult corner that would seem to have ruled out using the submarine, he said it was "specifically designed to pass that point".

Mr Musk also said that his submarine plan was encouraged by people working on the rescue. And he said that Mr Osatanakorn, who the BBC had described as a "rescue chief" because he is working to co-ordinate efforts, was not in a position to judge the plan.

"The former Thai provincial governor (described inaccurately as 'rescue chief') is not the subject matter expert," Mr Musk wrote. "That would be Dick Stanton, who co-led the dive rescue team."

He then shared what he said were emailed from Richard Stanton, one of the British divers who have been called in to help on the work. In those messages, Mr Stanton appeared to encourage Mr Musk to keep working on his designs.

"It is absolutely worth continuing with the development of this system in as timely a manner as feasible," one of the messages reads. "If the rain holds out it may well be used."

In response to Mr Musk's questions about whether it is definitely worth flying the submarine to Thailand, the messages from Mr Stanton reads: "We're worried about the smallest lad please keep working on the capsule details".

In the end, Mr Musk appears to have flown with the capsule to Thailand, and left it with those working on the rescue effort.

But it was not needed, and all of the Thai football team and their coach were evacuated using a method that involved two divers escorting each of them out to swim through the tunnels, despite the fact that some of the boys were not even able to swim.