"Negotiations were done very much with the personal engagement of the High representative [Catherine Ashton] who traveled there last night," her spokesperson Michael Mann told reporters in Brussels.
"They [the Bosnian Serbs, or Republika Srpska] are not going to go ahead with a referendum"
"We are very pleased," he said.
According to Mann, the Bosnian Serb authorities agreed that a "structural dialogue" on judiciary issues would be held instead of a referendum. The dialogue's first session will be held in early June, under the chairmanship of Enlargement Commissioner Stefan Füle.
Earlier this month, the parliament of Republika Srpska 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 crime suspects and ease the burden on the Hague-based International Criminal Tribunal for the Former Yugoslavia.
Analysts have described the referendum as a Serb attempt 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.
In recent weeks, the European Union's envoy to the Balkans strongly criticised plans for a referendum on the legality of Bosnia's national court, saying the "irresponsible" vote would widen divisions in the fragile nation.
Bosnia's international High Representative Valentin Inzko recently said that the planned referendum was the "most serious challenge" to Bosnia's viability since the end of the Balkan country's 1992-95 war (see background).
Inzko who so far has rarely used his powers to impose laws or fire obstructionist officials, said that all options are now open, including the replacement of Milorad Dodik, leader of Republika Srpska.
"The international community's support that I have could include the replacement of Dodik," he was quoted saying by Reuters.
"We are not going to fulfil Dodik's conditions," he said. "He must fulfil our conditions."