Of 10 alleged extremists arrested Wednesday, four were released on Thursday and the remaining six walked free on Friday, the official said.
Wednesday's raids were carried out in the southern port city of Marseille as well as Roubaix near the Belgian border, and in several other locations in the country's south and southwest.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
They came less than a week after 19 alleged Islamists were arrested in similar anti-terrorist swoops on Friday. Prosecutors have announced that they will seek terror charges against 13 of them.
French authorities have vowed a crackdown on Islamist extremists after self-confessed Al-Qaeda follower Mohamed Merah was shot dead in a police siege following a killing spree in which he murdered seven people.
The killings came just weeks before France's hotly contested presidential election, with security a major campaign theme and President Nicolas Sarkozy closing the gap in opinion polls on his rival, Socialist Francois Hollande.
Sarkozy's camp has been accused by some of its opponents of exploiting fears and stage-managing militant arrests for political gain.
