Police carried out raids across France on Saturday after DNA on a grenade that exploded at a kosher grocery story led them to a suspected jihadist cell of young Frenchmen recently converted to Islam.
The man whose DNA was identified, named by police as Jeremy Sydney, was killed by police after he opened fire on them, wounding three officers in the eastern city of Strasbourg. Their injuries weren't believed to be serious.
Ten other people, aged between 19 and 25, were arrested across the country. One man was carrying a loaded gun.
Paris prosecutor Francois Molins said all the arrested suspects were French. Four of the men involved in the raid had written wills. He added that police were still looking for one or two suspects.
A statement from President Francois Hollande praised the police for the raids and said the state would continue to "protect the French against all terrorist threats."
Last month's firebombing of the grocery, in a Jewish neighborhood outside Paris, happened on the same day that a French satirical paper published crude caricatures of the Prophet Muhammad, and while anti-Western protests were growing against an anti-Islam film. One person was slightly injured, but the attack came after a summer of what residents described as growing anti-Semitic threats.