Officers surrounded the archaeology museum in the Mediterranean town of Saint-Raphael, in the Var département, where the man broke in overnight and refused to communicate with police.
One of the messages reads “the museum is going to become a hell,” the source said.
#Intervention de police rue de la vieille église à St Raphaël.
Circulation difficile. Evitez le secteur.
Merci de ne pas gêner le travail des policiers et ne relayez pas de fausses informations. pic.twitter.com/Q24YjQhRkY
— Police Nationale 83 (@PoliceNat83) October 23, 2019
According to French TV channel BFMTV, the alarm was raised by a cleaner who discovered an Arabic inscription on the front of the museum when she arrived for work at 8am on Wednesday.
In a Twitter message police warned people to avoid the area in the historic centre of the resort town tucked between Cannes and Saint-Tropez.
“The entire neighbourhood is locked down… We've been ordered to stay in the restaurant,” Sebastian, an employee at the Duplex restaurant opposite the museum, told the local Nice-Matin newspaper.
Local prosecutors say they are remaining cautious about the man's motives.