Hundreds of military personnel are being deployed throughout Greater Paris following a mass shooting at at the offices of Charlie Hebdo that left 12 people dead and 11 more injured. In a statement Wednesday, France's interior minister, Bernard Cazeneuve, said 16 security units and mounted police squadrons have already been deployed in the city and its surrounding districts. The security units, he said, will be joined Thursday by 150 additional military forces, who will then be joined by 200 more from the France Ministry of Defense.

All told, a team of more than 800 military personnel will be working alongside local security and police squadrons to ensure the city’s safety and assist with the investigation, Cazeneuve said.

“The minister would like to reassure citizens that the entirety of Ministry of Interior personnel has been mobilized to work on both the ongoing investigation under the authority of the Procureur of the French Republic and the security measures implemented on the whole territory,” the statement read.

Cazeneuve also urged French citizens to “keep a cool head” and display “solidarity and unity” in the wake of the tragedy, which sparked demonstrations throughout the city and in cities around the world.

The attack took place Wednesday in Paris’ 11th arrondissement at the offices of Charlie Hebdo, a satirical magazine, where masked gunmen armed with AK-47s killed a number of staffers, including Stephane “Carb” Charbonnier, the magazine’s editor-in-chief. Two police officers guarding the building were also killed. The publication is thought to have been targeted for its history of publishing cartoons mocking the Islamic Prophet Muhammad. French officials identified brothers Said Kouachi, Cherif Kouachi and Hamyd Mourad as the suspects.

The minister’s statement went on to express grief for the “victims of this barbaric act, notably to the two police officers, who paid for their commitment to serving our citizens with their lives.”

Alessandria Masi contributed reporting to this story.