Western security officials have now concluded that these operations, and potentially many others, are part of a coordinated and ongoing campaign to destabilize Europe, executed by an elite unit inside the Russian intelligence system skilled in subversion, sabotage and assassination.
The group, known as Unit 29155, has operated for at least a decade, yet Western officials only recently discovered it. Intelligence officials in four Western countries say it is unclear how often the unit is mobilized and warn that it is impossible to know when and where its operatives will strike.
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,
widely known as the G.R.U.
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In 2006, Mr. Putin signed a law legalizing targeted killings abroad, the same year a team of Russian assassins used a radioactive isotope
to murder Aleksander V. Litvinenko, another former Russian spy, in London.
Unit 29155 is not the only group authorized to carry out such operations, officials said. The British authorities have
attributed Mr. Litvinenko’s killing to the Federal Security Service, the intelligence agency once headed by Mr. Putin that often competes with the G.R.U.
Although little is known about Unit 29155 itself, there are clues in public Russian records that suggest links to the Kremlin’s broader hybrid strategy.
A retired G.R.U. officer with knowledge of Unit 29155 said that it specialized in preparing for “diversionary” missions, “in groups or individually — bombings, murders, anything.”