Austrian media reports the young soldier was shot by a superior officer during an argument.
A soldier was killed and another injured after an exchange of fire at a military barracks in Austria.
The incident happened in the town of Wiener Neustadt, close to the border with Hungary in southeastern Austria, on Friday morning shortly before 07:00 CET.
"A 20-year-old guard from Lower Austria in the guard room of the airfield barracks in Wiener Neustadt fired shots with the assault rifle," Defence Ministry spokesperson Michael Bauer wrote on Twitter.
"He attacked and injured his superior. The superior fired a pistol shot, killing the soldier."
Austria's Federal Ministry of Defence gave more details in a statement mid-morning, saying that several shots were fired during the incident.
"A 20-year-old conscript from Lower Austria threatened his comrades during the changing of the guard and physically attacked his superior, the officer of the day, a 54-year-old non-commissioned officer."
The sergeant who was shot was taken to hospital for treatment, and an investigation has been launched by Austrian authorities into exactly how events unfolded.