Authorities in Montenegro have claimed Russian nationalists had planned to assassinate the country's prime minister because of his pro-Nato and pro-EU tendencies.

The Balkan country's chief special prosecutor, Milivoje Katnic, said "nationalists from Russia" had organised a group that had planned to break into the country's parliament on the day of the country's elections on 16 October, kill the prime minister, Milo Djukanovic, and bring a pro-Russian coalition into power.

Katnic said there was no evidence of Russian government involvement in the alleged plot although 20 Serbian and Montenegrin citizens, have been arrested, accused of trying to stage the coup. The Kremlin has denied involvement.

Katnic, who is the country's special prosecutor for organised crime and corruption, said the plot was for 500 people to "cause violence [...] and hire professional sharpshooters to kill the Prime Minister."

"The organisers are Russian nationalists. The aim was to stop Montenegro on its Euro-Atlantic path and in particular joining Nato," he said, according to agencies.

Soon after the ballot, Djukanovic announced he would quit as prime minister, although his office said the resignation has "nothing to do with the alleged coup", Radio Free Europe reported. Djukanovic is still in power.

Kremlin spokesman Dmitry Peskov, said, according to Interfax: "We categorically deny the possibility of involvement in any attempts to organize illegal actions."

However, Moscow has been accused of supporting parties opposed to Djukanovic's goal of bringing Montenegro into the European Union and Nato.

The alliance formally invited the ex-Yugoslav country to join in December 2015 and it signed an accession protocol in May 2016 and hosted a NATO drill last week.

Soon afterwards, a joint military drill involving Serbian, Russian and Belarusian armies entitled Slavic Brotherhood, started near the Serbian capital, Belgrade and will run until 9 November.

Nato's secretary-general, Jens Stoltenberg, said hundreds of thousands of Nato troops are on a high state of alert to counter Russia which he says is "implementing a substantial military build-up over many years."

Sir Adam Thomson, the UK's outgoing permanent representative to Nato, said that he believed the target is to hasten the response time of up to 300,000 military personnel to about two months, The Times reported.