France has deployed thousands of police to hunt down masked gunmen who shot dead 12 people in an attack on a satirical magazine in Paris on Wednesday that was one of the deadliest terrorist assaults on European soil in recent years.

The apparently well-planned attack on the offices of Charlie Hebdo, under police protection for years because of its repeated mocking of Islam, followed months of warnings by the French government of the risk of terrorism from Islamist militants.

Two gunmen entered the magazine’s offices on Wednesday morning, opening fire with automatic weapons. Eight journalists, including four of Charlie Hebdo’s best-known cartoonists, and two policemen were reported to be among the dead. The attackers escaped in a car, later found abandoned in the northeast of the capital.