Police in Montenegro have arrested 20 Serbs for allegedly planning to carry out armed attacks after polls close in the country's tense parliamentary elections.

Authorities said those arrested planned to collect automatic weapons to attack state institutions, police and possibly state officials following Sunday's key vote that could determine whether Montenegro continues on its Western course or turns back to traditional ally Russia.

The prosecutor's office said the group of Serbs, who were arrested on Saturday, planned to assault people who would gather in front of the parliament when the vote results were proclaimed, then storm the building in the capital Podgorica and declare the victory "of certain parties" in the election.

The statement said the group of Serbs also planned to arrest Montenegro Prime Minister Milo Djukanovic.

READ MORE: Thousands demand Montenegro PM resign as clashes rage

Police Director Slavko Stojanovic said they were charged of "arming a criminal organisation and terrorism". He said one Serbian is still on the run.

The announcement came amid the crucial Sunday polls, which pits Djukanovic's Democratic Party of Socialists against a cluster of pro-Russian and pro-Serbian opposition groups that staunchly oppose the government's pro-Western policies, especially its bid to join NATO.

As of 15:00 GMT, Al Jazeera's Milica Marinovic, reporting from the Podgorica, said an estimated 50 percent of the total number of voters had cast their ballots.  

The pro-Russian opposition heavily criticised the announcement of the arrests as propaganda, while Serbian Serbian Prime Minister Aleksandar Vucic said he had no information about the incident.

Police in Montenegro said one Serbian is still on the run [Reuters]

Fears of violence

There have been fears that violence could erupt on the streets of Podgorica between opposition and government supporters, after the results of Sunday's vote are announced.

The government also said hackers have attacked several websites, including that of the ruling party.

Djukanovic's ruling party faces a tough test in the polls, hoping its promise to bring the country into NATO and closer to the European Union, will outweigh allegations of corruption.

Montenegro invited to join NATO

The opposition said accusations that they are funded by Russia are false and a smokescreen to cover the corruption during Djukanovic's more than a quarter century rule.

NATO invited the tiny Balkan country of 650,000 to join last year, partly out of concern at Russian influence in Montenegro, which has strong cultural and commercial links to its traditional Orthodox Christian ally.

A lack of reliable polls makes the election hard to call, but long-term allies have deserted Djukanovic, suggesting the message from opposition parties may have traction.

The former Yugoslav republic's economy has grown at a brisk 3.2 percent a year for the past decade, thanks mainly to foreign investment, much of it from Russia as well as China and Italy, targeting energy, mining and tourism in a country famed for its spectacular mountains and sea coast.

At an opposition rally in the capital Podgorica on Saturday, hundreds of backers of the Democratic Front (DF), an alliance of pro-Serb and pro-Western parties, waved Serb, Russian and Montenegrin flags, chanting their campaign slogan "Us or Him".

"Djukanovic, step down peacefully on Sunday if you love Montenegro," said Nebojsa Medojevic, a pro-Western politician and one of the DF's leaders.

Polling stations close at 18:00 GMT, with first partial results expected an hour later.

Source: Al Jazeera News And Agencies