BELGRADE (Reuters) - Serbia has detained a number of people over a suspected plot to sway the outcome of Montenegro’s Oct. 16 election, the Serbian prime minister said on Monday, citing “undeniable and material” evidence found by his country’s security services.Aleksandar Vucic’s remarks were the first detailed Serbian reaction to the arrests on election day in Montenegro of 20 Serbian citizens, including a retired police general, accused of planning attacks on government institutions and officials.

The vote, in which veteran Prime Minister Milo Djukanovic’s party came out ahead but without a parliamentary majority, was billed as an opportunity for voters to endorse his pro-NATO and pro-EU stance instead of pursuing closer relationships with traditional allies like Serbia and Russia.

Vucic told a news conference that the evidence found included 125,000 euros ($135,975) in cash and stashed uniforms that were to be used in attacks on Montenegrin state institutions and individuals. Supportive evidence had been given by detained suspects under questioning, he said.

Vucic gave no details of the nature of the attacks planned on Oct. 16. He also did not name the suspects Serbian authorities had found, some of whom were in custody, but said they were not the same as those arrested in Montenegro.

“We have undeniable evidence that certain individuals, and they are certainly not those arrested down there, have been following movements of the Montenegrin prime minister and informing other people about them,” Vucic said, adding that other groups might yet be found.

“We could not find evidence of involvement by Serbian or Montenegrin politicians,” he added.

Serbia and Montenegro, its tiny neighbor on the Adriatic coast, are both former Yugoslav republics whose governments are seeking closer ties with the European Union and NATO against the wishes of some opposition nationalists and leftists.

Before the election, Djukanovic told Reuters that Russia was financing the opposition in order to derail Montenegro’s imminent NATO membership. Opposition parties, many also pro-NATO, deny this and reject the outcome of the “rigged” vote.

Cyber attacks shut down media and party websites and Montenegrin authorities suspended instant messaging services for much of election day, saying illegal “direct marketing” - believed to refer to opposition campaigning - was taking place.

While election observers found that the outcome broadly reflected “the will of the people”, Djukanovic, who has dominated Montenegro’s political life for a quarter for a century, has been accused of authoritarian tendencies.

His Democratic Party of Socialists, which won 36 seats in the 81-member parliament, is seeking allies to build a majority coalition, but it remains unclear if other parties will support him.

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