Around 20 personnel were involved in a training exercise at a Highland military base when a soldier was shot dead.
Police remain at Tain Bombing Range after the soldier was killed at around 6pm yesterday.
The base was locked down and roads in the surrounding area were closed off.
Police Scotland said a firearm was involved in the death of a member of the Armed Forces and that there were no other casualties.
Chief Inspector Iain MacLelland said around 30 detectives are involved in the investigation.
He added that the victim’s name would not be released at this time and he was not from the local area.
He said: “Police Scotland can confirm that just before 6pm last night, we received a call from the Scottish Ambulance Service reporting an incident at the RAF Tain firing range involving members from the Armed Forces who were on a training exercise.
“Police along with the Scottish Ambulance Service attended there, where one person was found to be fatally injured.
“There were no other casualties as a result of this incident and their next of kin have been informed.
“Both the police and the military are providing them with support at this time and our sympathies are obviously with them in what must be an extremely difficult time for the family.
“Police Scotland are leading the investigation to establish the full set of circumstances of this incident and we are working closely with the Crown Office and Procurator Fiscal Service, the Health and Safety Executive, and the Armed Forces.
“I would wish to emphasise that this incident was confined to the RAF firing range at Tain, that no persons were involved other than those military personnel participating in the exercise, and at no stage was there a threat to the wider public safety.
“The nature of this incident will require a continued police presence in the area over the days ahead and we would ask for the local community’s co-operation and we will continue to keep them updated.
“We are keeping a very open mind into the cause of the incident. It is the very early stages of the investigation and as the investigation progresses we’ll continue to release further information into the nature of that inquiry.”