By Jemima Kelly

LONDON (Reuters) - An infantry soldier died during a training exercise in the mountainous Brecon Beacons area of Wales on Tuesday, the hottest day of the year.

The Ministry of Defence (MoD) said on Wednesday a police investigation and military service inquiry would be carried out.

"It is with great sadness that I can confirm that an infantry soldier has died in Brecon while conducting pre-course training before attending the Platoon Sergeants’ Battle Course," junior defense minister Mike Penning said in a statement.

"The safety of our personnel is our absolute priority and, while deaths in training are rare, any death is a tragedy.... My thoughts and prayers are with the soldier’s family, friends, and colleagues at this difficult time."

The BBC said the soldier was a 26-year-old man from the Rifles regiment.

Three soldiers died in the same region during a grueling Special Air Service (SAS) cross-country selection test on one of the hottest days of 2013.

Earlier this year, British health and safety officials said they would give the MoD a "Crown Censure" over those deaths.

A coroner overseeing an inquest into the deaths last year said there had been a catalogue of mistakes, the risk assessment for the march had not been adequate and the response to the incident had been chaotic.

Temperatures in Britain on Tuesday were the hottest of the year so far, the Met Office said, reaching above 30C in many places. The highest July reading ever recorded in the UK was 36.7C (98F) last year.

The hottest temperature ever recorded in Britain was 38.5C (101.3F) in Faversham, Kent, in August 2003.

(Reporting by Jemima Kelly; editing by Stephen Addison)