There's a deeply classified unit of Russia's GRU (Chief Intelligence Department, - 112 International) that operates in Europe and may be involved in several high-profile operations. They include poisonings of the Skripals and Bulgarian businessmen Emilian Grebev, as well as the attempt of coup d'etat in Montenegro. The New York Times reported that with the reference to special services in four countries.
Special services came to the conclusion that these operations are a part of a coordinated and ongoing campaign to destabilize Europe. According to the medium, the special ops unit 29155 has been active for a decade, but it only became possible to track its actions just now.
"The purpose of Unit 29155, which has not been previously reported, underscores the degree to which the Russian president, Vladimir V. Putin, is actively fighting the West with his brand of so-called hybrid warfare — a blend of propaganda, hacking attacks and disinformation — as well as open military confrontation (...) Hidden behind concrete walls at the headquarters of the 161st Special Purpose Specialist Training Center in eastern Moscow, the unit sits within the command hierarchy of the Russian military intelligence agency", reads the article. "Last year, Robert S. Mueller III, the special counsel overseeing the inquiry into Russian interference in the 2016 elections, indicted more than a dozen officers from those units, though all still remain at large. The hacking teams mostly operate from Moscow, thousands of miles from their targets. By contrast, officers from Unit 29155 travel to and from European countries. Some are decorated veterans of Russia’s bloodiest wars, including in Afghanistan, Chechnya and Ukraine. Its operations are so secret, according to assessments by Western intelligence services, that the unit’s existence is most likely unknown even to other G.R.U. operatives".
The outlet quoted a former GRU operative who told it that the team 29155 is considered experts in terms of acts of sabotage that are carried out in groups or individually - "explosions, murders, whatever". "Some serious guys served there. They were officers who worked undercover, as well as international agents", the interlocutor said.