French police are investigating a suspicious letter addressed to the interior minister that tested positive for the plague, Paralel.Az reports citing The Telegraph.

Discovered at a mail-sorting centre near Dijon, the letter was addressed to the town hall of Roubaix, in the north of France outside Lille, for the attention of Gérald Darmanin, the minister of the interior.

Police were called when the unstamped envelope, with undisclosed “inscriptions” on its back, roused suspicions among workers. Inside, they discovered a black powder and a letter containing racist insults.

Preliminary tests – carried out by the police unit that deals with chemical, biological, nuclear, radiological and explosives matters – revealed a “slight positivity for the plague”, the disease that killed millions of people in Europe during the Middle Ages.