A soldier with the Royal Marines has died during a routine training exercise in the Brecon Beacons.
The Ministry of Defence (MoD) confirmed that Benjamin Poole, a signaller with the elite unit, died on Monday.
An MoD spokesman said the cause of his death was unknown and it would be inappropriate to comment until a post- mortem examination had been completed.
His death is being investigated by Dyfed-Powys Police and the Health and Safety Executive.
An MoD spokesman said: "We are very saddened at the death of Marine Benjamin Poole and our thoughts are with his family at this difficult time.
"Marine Poole, a Royal Marines signaller, died while undertaking a routine UK Military training exercise on 28 July 2008.
"The cause of Marine Poole's death is not known at this time and it would be inappropriate to comment further."
He said that they were cooperating with the police and health and safety investigation which is underway and said the family of Mr Poole had appealed for privacy.
Brecon Mountain Rescue Team was called out to the incident in the western Beacons, but was stood down before arriving at the scene.