A dentist in the centre of Marseille was shot dead Tuesday by a patient, a man in his 70s who was himself killed during the subsequent police intervention.
Police sources said the pensioner, who had been involved in a legal dispute with the practice, had turned up at the surgery with two handguns, a pistol and a revolver.
Witnesses heard several shots, the building was evacuated and police called. The suspected killer of the dentist was shot dead after he opened fire on officers, police said.
Although it appeared to be an isolated incident, Tuesday's shooting will add to Marseille's notoriety for gun crime.
At least four young men have been killed this month in execution-style shootings linked to rival gangs battling for control of the drugs trade in the southern port's rundown estates.
A total of 24 people died in similar circumstances during 2012, giving Marseille one of the highest murder rates in Europe and prompting calls from some politicians for the army to be sent in.