PODGORICA, Serbia-Montenegro — Montenegro voted by a slim margin to secede from Serbia and form a separate nation, erasing the last vestiges of the former Yugoslavia, according to the results Monday of its referendum.

With nearly all ballots counted, 55.4 percent of voters chose to dissolve Montenegro's 88-year union with its much larger and sometimes overbearing Balkan neighbor. That is just over the 55 percent threshold needed to validate Sunday's referendum under rules set by the European Union.

Hours before the official results were announced, independence supporters flooded streets of the capital Podgorica and other towns, even though their victory did not appear at all certain at that point.

"I congratulate you on your state," said the pro-independence prime minister, Milo Djukanovic.

In Podgorica, people fired celebratory shots in the air and drove up and down the main street, honking and waving the eagle-emblazoned flag used when Montenegro last enjoyed independence, from 1878-1918.

In Belgrade, the Serbian capital, officials urged calm. Ethnic Serbs make up 30 percent of the population and many strongly oppose separation from Serbia. Serbia did not want separation, but has said it will respect the decision.

The Serbia-Montenegro union is the last shred of the federation of Yugoslavia that began its blood-drenched breakup in the early 1990s. The division between anti- and pro-independence groups is deeply rooted in Montenegro's history, and some had feared violence no matter what the outcome.

In the former Yugoslavia's recent history, referendum results have sometimes led to major clashes and outbursts of nationalism. The Bosnian war started on the day that former republic voted for independence in early 1992, when its minority Serbs rebelled against the pro-independence government.