The presence of six British men trapped in a flooded Mexican cave for the past week has provoked a diplomatic row.
British soldiers rejected Mexican offers of help
Mexican President Vicente Fox wants to know why the cavers - five of whom are military staff - are on tourist visas.
The team, safe in a dry part of the cave, has rejected offers of help from Mexican rescue teams and are awaiting the arrival of UK military divers.
President Fox has instructed his foreign minister to seek clarification about the visas from the UK government.
A "note of protest" would be filed with the British government, he said.
"We are asking the British government to tell us whether these people are
military personnel, and if they are, what they are doing there."
The Foreign Office confirmed the Mexican ambassador to the UK would lodge a protest, but said: "This is strictly a caving expedition, has no other purpose and any
suggestions to the contrary are completely unfounded."
The acting British ambassador to Mexico, Vijay Rangarajan, dismissed concerns that the cavers were doing anything other than exploring as "pure fantasy."
"I think we just need to talk to the Mexican government and find out what
their problems are.
"If they're having problems down here, we'll have to look very carefully in
the future (to see) if any future permits are needed."
The Ministry of Defence said the men were there during a combined services
adventurous training expedition and were not on exercise.
Stephen Whitlock, one of the team above ground, said that although it was an official military expedition to support "adventurous training", the team was there to map the cavern system.
He added: "You've got to disassociate the fact that we're here as military".
Views differ about the need for visas, with a spokesman for Mexico's National Migration Institute saying scientific or exploration teams required special visas in Mexico and laws forbade training exercises by foreign military forces.
However, Mr Whitlock said: "There are no registration requirements for the sport
of caving and cave expeditions in the state of Puebla."
Mexican army troops and officials from the migration institute were on hand
and had interviewed the Britons about their visa status.
Two divers from the Cave Rescue Organisation - one of whom has extensive experience of the Cuetzalan cave system - flew to Mexico from London on Tuesday morning.
Soldiers in Mexico guard the cave where six British men are trapped
They will assess the flooding of the network of about 300 caves and passageways in eastern Mexico.
The trapped men are about a 35-minute walk from the entrance, said Ministry of Defence spokesman Gordon Mackenzie.
They have supplies of food and water and are said to be in good spirits.
If the flood waters do not subside, the divers will take in cave-diving equipment for the men so they can scuba-dive their way out.
The six men have not been officially named, but the brother of one of them, Chris Mitchell, told BBC News Online he was "concerned" about his sibling.
However, Phil Mitchell, 43, a finance director in Palma de Mallorca in Spain, added: "Chris is very well trained and will have been fully prepared for this type of event."
Have you been caving in the Cuetzalan system? Are you familiar with this area? Or have you been in this situation before? Send us your comments using the form below.
British servicemen and women undertake adventure training all over the world, usually as part of an in-service club or association. These are never conducted as military exercises and often include charitable work - I've personally worked alongside British military personnel in Patagonian Chile with Raleigh International. They didn't need any kind of special permission and like these cavers, they certainly weren't on any kind of "mission". Would Mexican military personnel have to get special visas to go camping in the UK? Of course not, and the Mexican Government and media should stop this wild speculation!
Jim Watkins, London, UK
I think some of the people making comments on here do not understand some of the background facts. British Military often arrange "holiday's" for its staff, in the same way that my employer (not military) has a ski club, rugby club and lots of other societies that arrange trips abroad. The majority of the people on this trip are military personnel but at least one is a civilian and they are all on leave. Also they where aware that the cave could flood and they have food, water and communications already set-up in case a flood occurred and are apparently in no real danger. I am sorry to see the responses from the non-GB people and i hope that the British take a less arrogant view when any of their citizens are in trouble.
Daren, Norfolk, United Kingdom
I would like to hear from the MOD if these cavers were in Mexico whilst on leave (during their own time) or whether they were there during MOD time? Once this is established we can then debate whether a tourist visa or something more official was required. If this was a combined forces training exercise as stated by the MOD, we should ask if any foreign governments could carry out training exercises within the UK whilst here on 'holiday'!
John Furmanek, Broadstairs England
There is no sensible rescue plan which could be put into effect in this situation - by far the best thing to do is to simply sit and wait for the water to fall. The trapped team are in no danger and could easily sustain several weeks underground if they had to: the possibility of rain preventing their exit was foreseen and planned for. Any attempt at a rescue would be likely to put both the team and, more particularly, the rescuers in unnecessary danger. I speak as someone who, when co-ordinating a cave rescue, has had to make the decision to do this on one of the rare occasions when it has been necessary in the UK.
Nick Williams, Buxton, England
Typical British arrogance not taking Mexican help. Maybe if they took some local advice they wouldnt be in this mess. I hope the British government reimburses the Mexican authorities every penny.
Andy O, San Diego CA
As well as needing some help in that most basic caving skills: reading a weather forecast, the British military obviously could do with some training in diplomacy.
Joe, Grasse, France
I'm surprised that this "military" team has been here, "training" without any permission from the Mexican government. Wouldn't it be awkward, me caving below Buckingham Palace without making a little note for the British government.
Mindel Orozco, Mexico City
I really don't understand what these soldiers were doing in my country. "Unofficial" mission? They'd better have some real good excuse for the local immigration officers down there. I hope everything turns out well, though.
Carlos A. Gonzalez, Dallas, TX
Why does not the BBC report about the real reasons because this incident has caused some unhappiness between the local population and the federal government? What were the members of the British army doing in Mexican caves, where it is forbbiden to go in without any permission? Why did the local officials not know about any foreign military exercises? I think that the British government does not care much about other country's sovereignty. The British government should apologize for this disdain.
Santiago Ramirez, Stuttgart, Germany
Rain was not unexpected. The UK team just did not check the TV weather forecast properly. Cuetzalan is a very very humid area throughout the year, because winds from the Gulf of Mexico are stopped against the mountains in that area. Next time it will cause less trouble to hire a local guide than an "expert" who in fact knows very little.
Eduardo Rosales, Mexico City
My uncle is part of the caving trip trapped in the caves in Mexico and I hope he is ok, his family is concerned. Your coverage of the incident has been great, thank you. Look forward to them coming home soon.
Olwen Milton, Cheddar, England
I am familiar with the area and I explored some caverns with my Boy Scouts troop when I was a teenager.
Fortunately for these men, there no rainy season until July. But there is too much confusion regarding the real objectives of these cavers. The media is mentioning that the military were surveying the area for radon and uranium.
Rogelio Perez, Puebla, Mexico
Disclaimer: The BBC may edit your comments and cannot guarantee that all e-mails will be published.