The suspension of the 18 follows the indictment of 12 of their colleagues on Friday on charges of extortion and drug dealing.
Seven of the initial 12 have been imprisoned pending further investigation while the other five were released on bail.
The latest suspensions mean almost half of the 70-strong Anti-Criminial Brigade in northern Marseille are now under investigation in what is beginning to look like one of the most serious cases of police corruption in French history.
Most of the officers who have been charged or suspended were arrested last Tuesday. They are suspected of routinely stealing drugs and cash from dealers and of holding on to cigarettes confiscated from illicit sellers.
The prosecutor who pushed for action against them told Friday's indictment hearing that there was "overwhelming" proof of their guilt and described the unit they worked for as a "gangrene" in the French police.
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