Speaking at an extraordinary press conference, Buric said the HDSSB was receiving threats all the time, but that this one surpassed them all. He read out the letter and distributed it to the members of the press.

The letter was sent to the party's address in the eastern city of Osijek on October 29, allegedly from the northern Adriatic city of Rijeka.

Buric called on the Interior Ministry and Minister Tomislav Karamarko to do their best so that the author of "this morbid threat" could be found.

Buric said the party wanted to tell everyone who would like to get rid of it that it was not afraid and that it would not stop pointing to irregularities and criminal activities in Croatia.

He said the HDSSB stuck by Branimir Glavas, a party official imprisoned for war crimes, adding: "You will neither shut us up nor stop us from fighting for the interests of Croatia and (the) Slavonia and Baranja (region)."

Buric accused the interior minister of involvement in attempts to prevent Glavas from being issued a passport in order to prevent him from running in the upcoming parliamentary election.

Osijek-Baranja County Police Department spokeswoman Ivana Delas confirmed that the HDSSB reported receiving a threatening letter yesterday and that they forwarded the report to the relevant prosecutor's office.