Earlier this month, the parliament of Republika Srpska, the Serbian entity of Bosnia and Herzegovina, overwhelmingly backed plans for a referendum on the court and its prosecutor, saying both were biased against Serbians.
The court was established in 2002 mainly to prosecute war crimes suspects and ease the burden on the Hague-based International Criminal Tribunal for the Former Yugoslavia.
Analysts have described the referendum as a Serb bid to undermine Bosnia-wide institutions like the court and challenge the authority of Bosnia's international High Representative Valentin Inzko, who has the power to overturn laws and fire officials.
Inzko, an Austrian diplomat, said in a telephone interview on Friday that he would move to prevent Bosnian Serb separatists holding a referendum to challenge the legality of a national court, the latest of a range of Serb separatist moves in Bosnia.
"There are two possibilities. Either the Serb Republic does it [annuls the vote] or the international community will," he said. "I will have to act."
Inzko also said a March decision by EU governments to threaten separatists in Bosnia with sanctions - assets freezes and travel restrictions already used in countries such as Libya, Iran and Belarus - were a step in the right direction.
"We could reach the moment when using them would be necessary," he said.
Recent visits by top EU officials to Sarajevo were helping drive the pro-EU message, he said, adding that Bosnia should be able to apply for EU membership this year. The move is likely to happen only with tacit approval from Brussels, even though in theory any country can apply to join the EU.
"Absolutely," he said when asked if Brussels should give Sarajevo the go ahead for membership. "This would start a huge transformation process."
The EU so far appears reluctant. Diplomats in Brussels say the bloc would first want to see constitutional reforms in Bosnia and progress on state aid and national census laws.
EU governments have discussed stepping up the bloc's presence in Bosnia for months, but there is disagreement over how that would tally with the role of the international envoy, which was meant to be phased out over time.
(EurActiv with Reuters.)