Following a meeting with the Republika Srpska President Milorad Dodik on Sunday in Belgrade, Nikolić told a news conference that the Serbian delegation in the negotiations in Brussels had "run into a wall" because the talks centred on Kosovo's independence.
Serbia doesn’t recognise the independence of its former province.
The EU-facilitated talks aimed at ending the ethnic partition of Kosovo ended without results on 3 April in Brussels.
The Brussels talks are not about the status of Kosovo, but on loosening Serbia’s grip on the northern, Serb-populated pocket of Mitrovica.
Both Nikolić and Dodik, who is the leader of the Serbian entity of Bosnia and Herzegovina, are seen as nationalists.
Nikolić called the compromise proposal, made by representatives of the EU’s foreign policy chief Catherine Ashton, an “ultimatum”, but also said that it could be improved.
"The stance of the state leadership, which will be united, will be declared on 8 April, which is not going to be easy, because that thing in Brussels is not an offer, it is an ultimatum,” Nikolić said.
“This is how we think of it. Can it be made better, it can, does it have to be made better, it does, since under the pretext of abolishing parallel institutions someone is trying to cross out the [Kosovo] Serbs who figure in their calculations as a parallel nation," Nikolić said.
France more supportive of Serbia
Speaking in Paris on Thursday, Serbian Prime Minister Ivica Dačić, who represented his country at the Brussels talks, said the EU side had given Serbia until 9 April to answer the proposal. He also indicated that France had shown more understanding to Serbia’s positions that Ashton’s representatives.
According to Dačić, French Prime Minister Jean-Marc Ayrault said that Paris would advocate for Serbia to receive a date for the start of EU accession talks as soon as possible and that France supported Serbia. Dačić explained that France had extended to Serbia “a hand which it can grab to get out of quicksand”.
Kosovo Prime Minister Hashim Thaci said on Thursday in Pristina that if there is no agreement, Serbia will suffer severe consequences, but Kosovo will not fare better either.
Thaci said the situation could deteriorate if no agreement was reached, and called for more work to be done on reaching an agreement with Serbia.
"We have come to an exceptionally significant phase, a decisive phase,” Thaci said, adding that the talks “are in the interest of peace in Kosovo, Serbia and the entire region."