A related article on what is known regarding Russian sabotage activities in Europe:
How and why Russia is conducting sabotage and hybrid-war offensive -- (Archived link)
Across Europe, we’re seeing more confirmed or suspected instances of Russian sabotage. It is part of a broader hybrid war campaign against NATO countries, aimed at eroding support for Ukraine and damaging Western cohesion [...]
Russia has conducted arson attacks in Poland, Germany, Lithuania, Latvia and Czechia. Other reported sabotage attempts include flying drones over Stockholm airport, jamming of Baltic countries’ civil aviation GPS systems and disruption of French railways on the first day of the Paris Olympics. Facilities linked to supplying Ukraine have also been targeted: a BAE Systems munitions facility in Wales, an air-defence company’s factory in Berlin and a Ukrainian-owned logistics firm in London.
Authorities have arrested suspects for plots to bomb or sabotage a military base in Bavaria and a French facility supporting Ukraine’s war efforts. Agencies disrupted a plot to assassinate the CEO of German arms maker Rheinmetall, a supplier of artillery shells to Ukraine. Latvian authorities tracked down saboteurs dispatched to several countries on paid missions. Norway’s domestic intelligence service warns of the threat of sabotage to train lines and to gas facilities supplying much of Europe.
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The West is running out of non-military options for response, since it is already imposing extensive economic and diplomatic sanctions against Moscow and has limited capacity or opportunity to retaliate in kind inside Russia. Still, a more strenuous response by Western governments is needed.
[Edit typo.]