US intelligence discovered earlier this year that the Russian government planned to assassinate the chief executive of a powerful German arms manufacturer that has been producing artillery shells and military vehicles for Ukraine, according to five US and western officials familiar with the episode.

The plot was one of a series of Russian plans to assassinate defense industry executives across Europe who were supporting Ukraine’s war effort, these sources said. The plan to kill Armin Papperger, a white-haired goliath who has led the German manufacturing charge in support of Kyiv, was the most mature.

When the Americans learned of the effort, they informed Germany, whose security services were then able to protect Papperger and foil the plot. A high-level German government official confirmed that Berlin was warned about the plot by the US.

For more than six months, Russia has been carrying out a sabotage campaign across Europe, largely by proxy. It has recruited local amateurs for everything from arson attacks on warehouses linked to arms for Ukraine to petty acts of vandalism — all designed to stymie the flow of weapons from the West to Ukraine and blunt public support for Kyiv.

But the intelligence suggesting that Russia was willing to assassinate private citizens underlined to Western officials just how far Moscow was willing to go in a parallel shadow war it is waging across the west.