Dunja Mijatovic cited the case of Tanja Jankovic, a journalist for B92 radio in Serbia.
On October 30 an explosive device was placed near Jankovic's parents' home.
The device failed to explode.
Mijatovic also pointed to an October 16 incident when unknown assailants threw a Molotov cocktail at the home of Damir Dragic, director of the "Informer" daily.
Mijatovic called on the Serbian authorities to "fully investigate" both attacks and to "ensure such attacks do not turn into a troublesome trend of violence against journalists."