Two servicemen have died during a training exercise in hot conditions in the Brecon Beacons in Powys.
A third man is in a serious condition in hospital following the incident late on Saturday afternoon.An investigation is taking place but it is understood live ammunition was not involved.
It is believed investigations will focus on the weather conditions and the nature of the training exercise.
The deaths occurred on the hottest day of the year so far in Wales with temperatures reaching 30C (86F) in Powys.
Matthew Dorrance
Mayor of Brecon
Next of kin have been informed, said the Ministry of Defence (MoD).
The MoD said in a statement: "The MoD can confirm that it is
working with Dyfed-Powys Police to investigate an incident during a
training exercise on the Brecon Beacons on Saturday in which two members
of military personnel died."The two servicemen's next of kin have been informed. More information will be released in due course but it would be inappropriate to comment further at this stage."
The Brecon Beacons forms one of Wales' national parks and is used for military training because of its relative remoteness.
The infantry regiments of the British Army train at Sennybridge in the area and there is an Army base in Brecon.
Mayor of Brecon and Powys county councillor Matthew Dorrance said: "It's incredibly sad for the friends and family of the people who have lost their lives and thoughts are with the person who is injured.
"In one way we've been blessed with the weather but for people working in this heat, they're tough conditions."
'Challenging terrains' Mr Dorrance said local people regularly saw troops training in the area and military vehicles parked on the side of the road.
"We're proud of our links with the milit