A Greek policeman is being questioned after a soldier providing Olympic security was shot dead, apparently after playing Russian roulette.
There is a huge security operation at the Olympics
The shooting took place before dawn on Monday, at the gates of an Olympic village at Mount Parnitha in Athens.
A 25-year-old soldier was shot in the forehead by a revolver that had held a single bullet, security sources said.
A 20-year-old policeman, described as a new recruit, was being questioned over the incident.
The policeman's partner on foot patrol at the time was also being questioned.
The AFP news agency named the victim as Antonis Syros, and the policeman under suspicion as Christos Chloros.
It quoted a written police statement saying the two men had been "jokingly" pointing the weapon at each other when it went off.
The forested region of Mount Parnitha is due to host the mountain biking events at the Games.
More than 100,000 security personnel are
involved in the operation to protect the Athens Olympics against the possibility of a terror attack.
The cost of the security has been put at more than a billion euros (£672m).