Montenegro is reportedly preparing to indict the Russian intelligence officer it accuses of masterminding a bloody coup plot to stop the Balkan nation joining Nato.

Eduard Sismakov, an officer with Russia’s GRU military intelligence service, is accused of running a web of Serbian and Russian nationalists and paramilitaries who plotted to assassinate the Montenegrin prime minister.

The British government believes the thwarted plot was carried out with the backing of Moscow and UK and US intelligence agencies have been helping the tiny Balkan nation unravel the conspiracy.

Another Russian GRU operative, using the name Vladimir Popov, is also being sought by Montenegro.