At least one man was holed up at a museum in southern France on Wednesday, where threatening messages in Arabic have been written on the building's walls, a police source told AFP.
Officers surrounded the archaeology museum in the Mediterranean town of Saint-Raphael, where the man, possibly with an accomplice, 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, without specifying if the man was armed or if other people were in the building.
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.
The museum, a historic monument, includes a medieval stone church and a vast collection of amphoras and other items from the region's Roman history.