Austrian diplomat Valentin Inzko, the UN High Representative in Bosnia who also holds various executive powers, made the decision last week.

Inzko imposed amendments to the Bosnia's criminal code to prohibit denial of genocide and war crimes in a country where the Srebrenica massacre is often played down by Serb leaders.

While the High Representative can pass laws or unseat elected officials, he has rarely used his powers in the past. This latest decision has outraged Serb politicians.

Branislav Borenovic, one of the opposition leaders in Republika Srpska, the Bosnian Serb entity, announced the boycott at a press conference.

"As of tomorrow, Serb political representatives will no longer participate in the work of the common institutions of Bosnia and Herzegovina and will not make any decisions until this issue is resolved," he told journalists.

Serb representatives will boycott Bosnian joint presidency, the parliament and the government, he added -- effectively blocking the central institutions that rely on the approval of representatives of all three ethnicities.

Ever since the 1990s war, which left about 100,000 dead, Bosnia has been divided into two entities, one Serb and the other Muslim-Croat.

- Inzko's successor disputed -

The Srebrenica massacre took place in July 1995, a few months before the end of the war, when Serb forces rounded up and killed more than 8,000 Muslim men and boys after capturing the town of Srebrenica.

The massacre was deemed genocide by various verdicts of both the International Criminal Tribunal for Former Yugoslavia (ICTY) and the International Court of Justice (ICJ).

Serb leaders in Bosnia and Serbia, however, usually deny the massacre amounted to genocide, instead calling it a "great crime".

Inzko's decision, which the diplomat made only a week before the end of his term, was immediately rejected by Bosnian Serb leaders.

Milorad Dodik, the Serb member of Bosnian joint presidency, has even threatened "dissolution" of the Balkan country.

The row comes at a particularly delicate time, as Inzko, after 12 years in office, prepares to hand over to Germany's Christian Schmidt on August 1.

But Russia and China are challenging Schmidt's appointment at the UN.

"The High Representative who arrives does not have legitimacy," Dodik told journalists on Monday.

And Mirko Sarovic, president of the main Serb opposition party SDS, said: "We will never again accept any decision (...) of the High Representative."

Bosnia's parliaments are the only places for decision-making, he added.