Chiang Rai, Thailand (CNN) A medical assessment of the 12 boys and their football coach stuck in a cave in Northern Thailand concluded that it was too dangerous to try to move the group out Thursday, according to a member of the Thai Navy SEALs who is not authorized to speak to the media.

The SEALs have started to pump oxygen into the chamber.

Separately, a new doctor's report highlighted that two of the boys and the coach were suffering with exhaustion from malnutrition.

Fresh details of the operation underway at the Tham Luang Nang Non to free the team were emerging, as rescuers pushed ahead with multiple plans to extricate the group trapped underground for almost two weeks.

More rain is forecast this weekend, putting pressure on rescuers to formulate a plan to extract the boys before flood waters rise any higher.

Huge volumes of water are being pumped out of the cave complex each day, but the narrow, winding passages inside are still flooded, meaning diving through the murky water is currently the only way in and out.

Rescuers entering the cave complex located in northern Thailand have to navigate dark, flooded tunnels for six hours to reach the team. It takes another five hours to return to the entrance.

An additional 30 SEALs arrived on site to reinforce rescue operations, according to Captain Supachai Thanasarnsakorn, deputy chief of the Thai Navy SEALs. They join the 80 already involved in the rescue operation comprising active, reserve and former SEALs.

Around the camp which has sprung up near the cave entrance, Thai military divers have set up an encampment with diving gear and equipment, while people from the local community hand out food to rescuers, other volunteers and the small army of press on site.

Trying to stop the water

The boys were in good spirits despite spending almost two weeks underground, Chiang Rai governor Narongsak Osottanakorn said.

"I confirm here again that they are in good health and they are smiling and playing around," he said.

International rescue effort Thailand may be leading the search to free 12 boys and their coach from a cave in the country's north, but many other countries are contributing assistance. Australia -- Australian police divers are taking part in rescue efforts and helping with planning. China -- Six rescue specialists from NGO Beijing Peaceland Foundation are assisting Thai divers. Israel -- Israel's Maxtech Networks is providing radio and communication equipment. Laos and Myanmar -- Thailand's neighboring countries each sent rescue workers and divers. UK -- Two UK divers were first to discover the boys, earning one a commendation from the British Cave Rescue Council. US -- US Indo-Pacific Command (PACOM) sent 30 military personnel, including divers.

The last images the world saw of the boys was on Wednesday in a video where they introduced themselves one-by-one, saying "I am healthy."

Since they were found late Monday local time by a duo of British expert cave divers , Thai Navy SEALs have stayed with the team, tending minor wounds and giving them food to build up their strength.

The boys remain weak after spending days in the darkness, barely moving from the small, muddy ledge, away from the water.

While rescuers are trying to pump enough water out of the cave to allow the boys to simply walk out, Thai Navy SEALs are also teaching them how to scuba dive.

The boys would need to wear full-face diving masks to enter the narrow tunnels in moving water, though many experts say this would be a dangerous option for novice divers.

In an attempt to maintain the boys' morale, rescue teams have prioritized installing a line of communication between the boys and their parents.

However, they were still attempting to connect them Thursday after earlier efforts failed when the line became damaged after falling into water. CNN saw an old-style military phone and loops of cable being carried into the cave by engineers.

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Search for other entrances continues

As divers work in tunnels deep below ground, teams are also scouring the hillside above the caves, looking for possible entry points to the chamber where the boys are sheltering.

"We are drawing our jungle trekking resources together. There are about 20 to 30 teams," Osottanakorn said.

"Now we are going to walk around that area to search every inch, (to see if) there are chimneys or holes where we can climb down, and we may adjust our plan."

The teams searching for another route through a natural chimney were dispatched following reports that the boys had told divers they heard dogs barking, a rooster crowing and children playing, possibly indicating a shaft leading up to the surface.

"There has been reports that kids have heard sounds from chickens and birds," Ben Reymenants, a Belgian who owns a diving shop in Thailand and has been assisting with the rescue efforts, told CNN.

"Were those hallucinations or did they really hear it? Because that would mean there is livestock nearby or at least a forest which would make an alternative entrance possible."

Osottanakorn said that teams on the surface were no longer drilling into the rock to create new shafts, but are focusing efforts on finding existing chimneys.

"We are no longer digging -- we will find a way that can give us access (without digging) direct to the area where the boys are," he said.

Rains a constant concern

Rescue coordinators are warily eying the skies for further downpours, which could imperil the rescue mission.

"In the previous days we were fighting with time. And now we are working against water," Osottanakorn said.

"We are draining out as much as our capacity allows. But water continues to flow in, no matter how many holes have been blocked, water still continues to pour in."

Osottanakorn said rescuers were at the mercy of the rainy season, and may have to act quickly to beat fresh downpours.

"If we must evacuate (the boys) out before they are ready due to the rain ... we will do so, but it will be the very last resort to do so," he said.

CNN Weather reports that while rain can't be ruled out, there is a likelihood that the area will remain relatively dry until at least Saturday. The chance of rainfall increases from Sunday, and alongside the increased rainfall is the threat of heavier downpours.

International efforts and support

Thai Navy divers have brought in substantial supplies -- including food and water for at least two weeks along with aluminum blankets, with support from Australian and other international divers, according to a statement from the Australian Federal Police (AFP).

The AFP's Specialist Response Group personnel are among the many divers and support staff who have been sent by a number of nations.

Photos: Photos: Thai soccer team rescued from cave Photos: Photos: Thai soccer team rescued from cave The rescued team attends a news conference in Chiang Rai, Thailand, after being discharged from the hospital on Wednesday, July 18. Hide Caption 1 of 54 Photos: Photos: Thai soccer team rescued from cave Members of the soccer team greet well-wishers as they arrive for the news conference on July 18. Hide Caption 2 of 54 Photos: Photos: Thai soccer team rescued from cave The team poses with a sketched portrait of Saman Kunan, a former Thai Navy SEAL who died on July 6 while returning from an operation to deliver oxygen tanks to the cave. He ran out of air while underwater, an official said. Hide Caption 3 of 54 Photos: Photos: Thai soccer team rescued from cave Thai Navy SEALs pose for a photo after the rescue effort was finished on July 10. One of them was a doctor who stayed with the team for a week after the group was found alive on July 2. Hide Caption 4 of 54 Photos: Photos: Thai soccer team rescued from cave Rescuers carry one of the boys out of the cave. Hide Caption 5 of 54 Photos: Photos: Thai soccer team rescued from cave Divers wave through floodwaters in the cave. Each rescue took multiple hours. Hide Caption 6 of 54 Photos: Photos: Thai soccer team rescued from cave Chiang Rai Governor Narongsak Osotthanakorn speaks during a news conference held after the rescue was finished on July 10. Hide Caption 7 of 54 Photos: Photos: Thai soccer team rescued from cave A helicopter transports rescued boys to the hospital on July 10. Hide Caption 8 of 54 Photos: Photos: Thai soccer team rescued from cave People watch and cheer as a helicopter flies toward an airstrip to transport one of the rescued boys to a hospital. Four boys were rescued on July 8, another four were rescued on July 9, and the rest were rescued on July 10. Hide Caption 9 of 54 Photos: Photos: Thai soccer team rescued from cave Rescue workers leave after all members of the team had been saved. Hide Caption 10 of 54 Photos: Photos: Thai soccer team rescued from cave This photo tweeted by tech entrepreneur Elon Musk shows rescue efforts during the three-day mission. Musk tweeted early July 10 that he had visited the cave and left a mini-submarine there for future use. Hide Caption 11 of 54 Photos: Photos: Thai soccer team rescued from cave Members of the Royal Thai Navy are pictured with the team inside the cave. Hide Caption 12 of 54 Photos: Photos: Thai soccer team rescued from cave The boys received medical attention after being found alive on July 2. Hide Caption 13 of 54 Photos: Photos: Thai soccer team rescued from cave An ambulance believed to be carrying one of the rescued boys heads to the hospital on July 10. Hide Caption 14 of 54 Photos: Photos: Thai soccer team rescued from cave Rescuers walk toward the entrance of the cave as rescue operations resumed on July 10. Hide Caption 15 of 54 Photos: Photos: Thai soccer team rescued from cave Hospital staff and a police officer are seen during a news conference that was held on July 10. The eight boys that had been rescued on July 8 and 9 were being treated in an isolation ward in a Chiang Rai hospital. Hide Caption 16 of 54 Photos: Photos: Thai soccer team rescued from cave Thai police and military officers use umbrellas to shield a rescued boy before he was transported to a hospital on July 9. Hide Caption 17 of 54 Photos: Photos: Thai soccer team rescued from cave An ambulance exits the cave area on July 9. Hide Caption 18 of 54 Photos: Photos: Thai soccer team rescued from cave Emergency responders surround a helicopter on July 8. Hide Caption 19 of 54 Photos: Photos: Thai soccer team rescued from cave Rescue teams arrange a water-pumping system at the cave's entrance on July 7. Hide Caption 20 of 54 Photos: Photos: Thai soccer team rescued from cave Ambulances wait outside a hospital where the rescued boys were treated. Hide Caption 21 of 54 Photos: Photos: Thai soccer team rescued from cave Thai military personnel walk into a cave during rescue operations. Hide Caption 22 of 54 Photos: Photos: Thai soccer team rescued from cave Military personnel work inside a cave. Hide Caption 23 of 54 Photos: Photos: Thai soccer team rescued from cave An ambulance leaves the scene of the rescue effort on July 8. Hide Caption 24 of 54 Photos: Photos: Thai soccer team rescued from cave This undated photo, released via the Thailand Navy SEAL Facebook page, shows rescuers with their hands locked. The caption said, "We Thai and the international teams join forces to bring the young Wild Boars home." The Wild Boars is the name of the soccer team the boys play on. Hide Caption 25 of 54 Photos: Photos: Thai soccer team rescued from cave Family members pray in front of a Buddhist statue near the cave on July 8. Hide Caption 26 of 54 Photos: Photos: Thai soccer team rescued from cave Emergency workers carry oxygen tanks as rescue operations begin. Hide Caption 27 of 54 Photos: Photos: Thai soccer team rescued from cave Thai soldiers work to connect pipes that help water from entering a cave. Hide Caption 28 of 54 Photos: Photos: Thai soccer team rescued from cave Thai forest rangers examine a map as they review their rescue options on July 8. Hide Caption 29 of 54 Photos: Photos: Thai soccer team rescued from cave This image, taken from video on July 2, shows the team trapped inside the cave. That was the day divers found them alive. Hide Caption 30 of 54 Photos: Photos: Thai soccer team rescued from cave Divers were able to bring food, blankets and other supplies to the boys while experts determined the best way to get them out safely. The team was found around two kilometers (1.24 miles) into the cave and somewhere between 800 meters to one kilometer below the surface, according to a British Cave Rescue Council briefing note. Hide Caption 31 of 54 Photos: Photos: Thai soccer team rescued from cave The team was found alive by British divers. The search brought rescue teams from all over the world. Hide Caption 32 of 54 Photos: Photos: Thai soccer team rescued from cave A Thai military medic provides first aid to one of the boys. Hide Caption 33 of 54 Photos: Photos: Thai soccer team rescued from cave The body of Saman Kunan, a former Thai Navy SEAL, is carried during a repatriation and religious rites ceremony on July 6. Kunan died Friday as he returned from an operation to deliver oxygen tanks to the cave. He ran out of air while underwater, an official said. Hide Caption 34 of 54 Photos: Photos: Thai soccer team rescued from cave Thai police take a break for breakfast as rescue operations continue on July 4. Hide Caption 35 of 54 Photos: Photos: Thai soccer team rescued from cave Water is pumped out of the cave on July 3. Hide Caption 36 of 54 Photos: Photos: Thai soccer team rescued from cave Workers fix the road leading to the cave on July 3. Hide Caption 37 of 54 Photos: Photos: Thai soccer team rescued from cave Divers prepare a light to be used for the underwater search on July 2. Hide Caption 38 of 54 Photos: Photos: Thai soccer team rescued from cave Rescue workers wait at the entrance to the cave on July 2. Hide Caption 39 of 54 Photos: Photos: Thai soccer team rescued from cave Some of the team's family members celebrate after receiving news that the team was alive. Hide Caption 40 of 54 Photos: Photos: Thai soccer team rescued from cave Technicians lift water pumps to the drilling site on July 1. Hide Caption 41 of 54 Photos: Photos: Thai soccer team rescued from cave Soldiers and rescuers work outside the cave complex on July 1. Hide Caption 42 of 54 Photos: Photos: Thai soccer team rescued from cave Monks attend a Buddhist prayer for the team on July 1. Hide Caption 43 of 54 Photos: Photos: Thai soccer team rescued from cave Scuba tanks are delivered to the search site on July 1. Hide Caption 44 of 54 Photos: Photos: Thai soccer team rescued from cave Rescue workers carry water-pumping equipment into the cave on July 1. Hide Caption 45 of 54 Photos: Photos: Thai soccer team rescued from cave A Thai Air Force worker drops near a possible cave opening on June 30. Hide Caption 46 of 54 Photos: Photos: Thai soccer team rescued from cave British cave diver Robert Charles Harper explores an opening on June 29. Hide Caption 47 of 54 Photos: Photos: Thai soccer team rescued from cave Relatives of the trapped team members pray on June 27. Hide Caption 48 of 54 Photos: Photos: Thai soccer team rescued from cave Family members waited more than a week for news of their loved ones. Hide Caption 49 of 54 Photos: Photos: Thai soccer team rescued from cave Thai soldiers bring hoses and additional water pumps as the search for the team continued on June 27. Hide Caption 50 of 54 Photos: Photos: Thai soccer team rescued from cave Volunteer paramedics wait near the cave entrance on June 27. Hide Caption 51 of 54 Photos: Photos: Thai soccer team rescued from cave A rescuer looks for a cave entrance on June 27. Hide Caption 52 of 54 Photos: Photos: Thai soccer team rescued from cave Rescuers search the cave on June 26. Hide Caption 53 of 54 Photos: Photos: Thai soccer team rescued from cave Thai soldiers relay cable at the search site on June 26. Hide Caption 54 of 54

The Australians on the ground "remain closely engaged in efforts to support and sustain the group, as well as in planning. This includes supporting the Royal Thai Navy to transport food, water and first aid supplies into the cave system through to the group."

They are part of an international contingent that includes teams from the US military, the UK, and China.

The Thai people got moral support from one of the 33 Chilean rescued miners who were trapped for 69 days in 2010.

"To the people in Thailand, I want to send you a message from a long distance, and also a lot of strength to the authorities and all the families of these 12 children who are trapped underground," Mario Sepulveda said in a video message.

"I have no doubt that if we pray, I have no doubt that if the government in Thailand gives all it has and makes all possible human efforts, this rescue will be a success," he said.