These took place "via social networking websites" and were made "by a so-called Black Hand (Crna Ruka) organization."

Stefanovic told a press conference on Tuesday the Serbian police were working together with the police of a country the threats were suspected of coming from "to identify IP addresses of potential perpetrators."

The minister said he expected to receive information from the police of that country very soon, adding that "the investigation would show whether the threats had been made by a single person or it was an organized network."

Black Hand said on its Facebook profile it was organizing a “public hunting” of Prime Minister Vucic, who, they said, had tried to get a revenge, via the Security Information Agency (BIA), on Radomir Pocuca, a former TV Pink host and a former spokesman for a special police unit, who was recently arrested in Ukraine where he was a volunteer fighter.

In the threatening notes, which contains insults at the expense of the prime minister, the Black Hand said that that all the people and resources available to the organization had been mobilized for the purpose of physically liquidating Vucic, the state-run Radio Television of Serbia (RTS) reported.