The coalition of pro-Serbia parties known as the Bloc for Joint State claimed that voters' lists contained names of people not eligible to vote, said Zdravko Gvozdenovic of Montenegro's Referendum Commission.
Gvozdenovic would not elaborate, pending the Commission's official response. If the Commission accepts the complaints, it could lead to a repeat vote in more than 100 polling stations - totaling some 100,000 voters - and possible reversal of the Sunday ballot whose preliminary results showed that the tiny Adriatic republic has opted to break away from much-larger Serbia.
The pro-Serbia groups lodged their complaints late Wednesday, just before a deadline to challenge the results.
The preliminary tally showed that in the tiny republic of 620,000 people, 55.5 percent of ballots cast were in favor of independence. That was just half a percentage point - or 2,090 votes - over the 55-percent threshold needed to validate secession under rules set by the European Union.
The leader of the anti-independence faction, Predrag Bulatovic, has warned of "negative consequences" unless the alleged irregularities are addressed. He also accused the rival side, led by pro-independence Prime Minister Milo Djukanovic of not allowing pro-union supporters to fully review the "suspicious" voters' lists.
Bulatovic has alleged that some 5,000 independence supporters, who reside outside Montenegro and therefore are not eligible voters, were illegally included in the voters' lists and took part in the Sunday ballot, giving Djukanovic's camp the critical edge, the AP reports.
Djukanovic has repeatedly insisted that the vote was transparent and urged his opponents to give up attempts to overturn Montenegro's split from Serbia.
In Serbia, where the government and most politicians had supported preserving the joint state, ultranationalist leader Tomislav Nikolic said the Montenegrin vote was "stolen" and accused the European Union of "assisting the theft."
After it turned out that Deputy Prime Minister Andrei Belousov included the Fonbet betting company in the list of backbone enterprises that can count on state support, everyone started talking about these bookmakers.