Oleg Deripaska, the Russian oligarch, was yesterday accused by the United States of working with a former Kremlin intelligence officer to interfere in Montenegro’s 2016 elections.

The US Treasury announced sanctions against Victor Alekseyevich Boyarkin, once a member of Russia’s GRU military intelligence agency but now working for Mr Deripaska, according to the department.

The Treasury said that Mr Boyarkin “reported directly to Deripaska and has led business negotiations on Deripaska’s behalf”. It added: “Deripaska and Boyarkin were involved in providing Russian financial support to a Montenegrin political party ahead of Montenegro’s 2016 elections.”

That election, it has been alleged, featured an assassination attempt on the country’s prime minister by the pro-Russian opposition to stop its accession to Nato. Russia has denied involvement, and it is not suggested Mr Deripaska or Mr Boyarkin were involved in the attempt.

The plot, reported extensively by The Daily Telegraph last year, has become a focal point for Western fears about Russian election meddling and led to legal action being taken against leaders of the Montenegrin opposition and two Russian nationals.