Russian military intelligence officers spent months overseeing a coup plot to overthrow Montenegro’s government and kill its prime minister, prosecutors in the small Balkan nation allege.

Eduard Shishmakov and Vladimir Popov of the GRU spy agency gave their plot ringleader large sums for weapons and equipment and he was also given a lie detector test to check he was not a Western intelligence agent, it is claimed.

A lengthy indictment against the plotters alleges the network was given sophisticated encrypted phones set up from Moscow, while at least one money transfer to the conspirators was made from the same street as GRU headquarters.

According to details of the Montenegrin government’s case seen by the Telegraph, prosecutors also say they have gathered surveillance evidence of the Russian officers meeting the Serbian radicals they hired to carry out the operation.

A total of 14 suspects, including two pro-Russian opposition leaders, face trial in the Montenegrin capital for terrorism offences over the alleged plot. The two Russians, who remain at large, are being tried in their absence.

British and US officials believe the conspiracy had high-level backing from Russia and claim it was one of the most audacious examples yet of the Kremlin’s escalating attacks on European democracy. Montenegro’s state prosecutors have in the past alleged the involvement of “Russian state bodies”.