Thousands of police will guard Jewish schools across France, while the military is also being deployed. Millions of people attended solidarity marches in France Sunday, including many world leaders.
Two brothers accused of killing 12 people on Wednesday are in phone contact with authorities in what has become a hostage situation. In another, possibly related incident, a gunman has taken a hostage in a kosher supermarket in Paris.
Two brothers, born in France to Algerian parents, are the subject of an intense manhunt focused on the Picardy region as France mourns the deaths of 12 people in Wednesday's assault on the offices of a satirical magazine.
A third suspect has turned himself in. Prime Minister Valls said several arrests had been made overnight in connection with the deadliest terror attack in France in a generation.
France was under heavy pressure from NATO allies not to go through with the sale of the helicopter carrier amid rising tensions over Ukraine.