"The evidence that has been gathered [on the incident] so far does not suggest that it was a terror attack," Brest Prosecutor Jean-Philippe Recappe said, as cited by the Franceinfo broadcaster.
Recappe also said that the Parisian prosecution's counterterrorism branch was not participating in the investigation into the incident.
On Thursday, the French RTL radio station reported that a gunman opened fire near a mosque in Brest, injuring two people, including the Imam.
The shooting occurred at around 4:00 p.m. local time (14:00 GMT). The gunman fled the scene but was found by police with a gunshot wound in his head. Following the incident, France's Interior Ministry ordered security be tightened at places of worship around the country.