"We condemn the sudden arrest of Jovic by the Croatian justice system based on a ICTY arrest warrant, which appears disproportionate to the crime he is accused of and sets a dangerous precedent," the worldwide press freedom organisation said.
"Considering the mandate of the tribunal in The Hague, which is supposed to try the most serious of international crimes, it is surprising that one of its decisions led to the arrest of a journalist who, even if he did not respect the law, has not committed a crime of violence," the organisation said.
"The same goes for the other four Croatian journalists also accused of contempt of court. Considering that this journalist represents no danger for Croatia and the ICTY, he should be released on bail." Reporters Without Borders said.
Journalist Josip Jovic was arrested on Thursday afternoon and taken to the District Prison in the southern coastal city of Split.
Earlier on Thursday a Split County Court investigating judge ordered that the former editor of the Split-based Slobodna Dalmacija daily be arrested based on an order from the Hague war crimes tribunal.
On 9 September the Hague tribunal charged Jovic with contempt of court for making public the identity and testimony of a protected witness in the trial of former Bosnian Croat military commander Tihomir Blaskic
After consultations with the International and European Federations of Journalists (IFJ/EFJ), the Croatian Journalists' Association (HND) on Friday urged the Hague war crimes tribunal to consider the possibility of discontinuing proceedings against Jovic and other Croatian reporters the tribunal charged with contempt.
The HND also called on reporters and HND members to abide by laws, regulations and decisions by Croatian courts and the Hague tribunal, it was said after an extraordinary session of the HND Executive Committee on Friday.