Tensions between Serbia and Montenegro have spilled over into the Eurovision song contest, which has a history of intense national rivalry.
Winners No Name from Montenegro were booed off the stage
An argument is raging over which band should represent the federation of Serbia and Montenegro in the contest.
A Montenegrin boy band called No Name won a televised competition in Belgrade to choose the best song - but they were booed by the audience, who cried foul.
The Montenegrin judges on the panel were accused of tactical voting.
After the vote on Saturday night the band took to the stage to sing their winning song again, but in the face of the mainly Serb audience's hostility, they soon gave up without having sung a note.
The Serb runners-up, Flamingoes, then appeared to the clear delight of the audience.
Passions were running so high at Belgrade's Sava Centre concert hall that the judges and the Montenegrin group had to be escorted out by security officials.
Speaking on Sunday, former Serbian Prime Minister Zoran Zivkovic said the furore had caused "much more excitement last night than the death of [former Yugoslav President] Slobodan Milosevic".
Flamingoes band members said the vote looked suspicious
A Flamingoes band member called Marinko told Serbian TV he was "totally convinced that some ulterior motives are at play here, in this area where there is no room for such things".
The BBC's World Media correspondent, Sebastian Usher, says the contest is being treated as a huge scandal in Montenegro.
The republic is due to hold a referendum in May on whether it wants full independence from Serbia. By coincidence it will be held the day after the Eurovision contest.
Several Montenegrin newspapers say the row shows that the federation with Serbia not only fails to work politically or economically, but cannot even function musically.
A viewer told Montenegrin TV that "the Belgrade audience should have shown some respect for the No Name band - their behaviour was really not on".