An Italian anti-terrorism unit is investigating graffiti on a wall in Milan inciting violence against Italy's firebrand interior minister, Matteo Salvini.

The blue lettering that appeared Thursday urges: "Don't shoot blanks. Shoot Salvini." It bears a red A inside a circle, a typical anarchist symbol, and the figure of Salvini in a law enforcement uniform.

Salvini responded to the threat saying, "nothing and no one scares me, or will stop me."

The call to violence was condemned by politicians across the spectrum, recalling the so-called "Years of Lead" from the late 1960s into the early 1980s, marked by left-wing and right-wing political violence.

Milan Mayor Giuseppe Sala, a member of the opposition Democratic Party, said the threats against Salvini "are not tolerable."