French police gather outside a local police station in Paris, France.

Three people have been charged with supplying arms to militants who staged deadly attacks in 2015 on a Jewish supermarket in Paris and the Charlie Hebdo satirical weekly, a judicial source said.

Those charged this week include Samir L., believed to be linked to the sale of weapons to the supermarket attacker, as well as Miguel M. and Abdelaziz A., who are thought to have been involved in trafficking arms between Belgium and France.

Seven people have already been charged over the assaults. The attackers had a wide array of weapons including guns that came from Slovakia.

Investigators are trying to piece together how France-based militant Amedy Coulibaly obtained the weapons used in the January 9, 2015 attack on the supermarket.

Coulibaly killed four people after taking shoppers hostage at the Jewish store. Elite police later shot him dead as they stormed the building.

He had killed a policewoman in the Montrouge suburb south of Paris the night before, when authorities think he may have initially been targeting a nearby Jewish school.

The attack was part of three days of terror in the French capital that began with the raid on the Charlie Hebdo satirical magazine offices that killed 12 people.