A man was shot dead and another was injured in a snack bar in the city late on Thursday night.
BFM TV reported that the attack was carried out with a Kalashnikov weapon.
The two victims were aged 41 and 32 reported newspaper 20 Minutes.
"This involved one shooter, perhaps with a second individual," said the public prosecutor, Jacques Dallest.
"He started shooting inside the bar, killing one man and seriously injuring one other who was seemingly an employee."
A total of 30 gun cartridges and bullet marks were found in the bar.
"We don't know if the dead man was a client or worked in the bar," he said.
The shooting rounds off a week of violence in the city which is known for its problems with crime.
On Sunday night a man was shot dead by police after a car chase in the town of Vitrolles, north of Marseille.
The next day a Romanian man was also shot dead by police after a burglary in the northern part of the city.
Interior minister Claude Guéant installed a new senior official, Alain Gardère, to combat crime in the city in August.
He also pledged a reinforcement of 360 additional police officers for the city, including 200 from the anti-riot CRS squad.