American intelligence agencies uncovered a Russian plot to kill the chief executive of a German weapons manufacturer, according to multiple western officials, as Moscow steps up a campaign to undermine support for Ukraine’s war effort.

The US warned Germany about the plot, and German officials increased protection for Armin Papperger, who leads Rheinmetall, which makes artillery shells and tanks that Ukraine has used in its war against Russia.

This year, Russian military intelligence has carried out a series of arsons aimed at disrupting the supply of weapons and other materiel to Ukraine, prompting the expulsion of undercover spies and warnings from Nato. The assassination plot is a significant escalation, officials said, representing a more concerted covert effort to deter western companies from producing supplies for Ukraine.

A senior western intelligence official said the threats were flagged this past spring. Papperger was the only defence industry figure who was targeted by name or for whom the Russians appeared to have developed an advanced plan for the assassination, officials said.

The officials spoke on the condition of anonymity to discuss the Russian operation.

The senior western intelligence official said the plan was advanced to the point where Papperger had taken protective measures. Other threats that targeted European defense industry officials were more vague, the official said.

The plot, and the US efforts to disrupt it, were earlier reported by CNN.

American, German and Nato officials would not comment on specifics of the plot, but they denounced Russia’s sabotage and hybrid-style attacks in Europe.

Russia has intensified its “campaign of subversion”, said Adrienne Watson, a spokesperson for the National Security Council, adding that the US has been discussing the covert attacks with its Nato allies.

“We are actively working together to expose and disrupt these activities,” Watson said. “We have also been clear that Russia’s actions will not deter allies from continuing to support Ukraine.”

The purpose of the Russian covert campaign is to intimidate the alliance from supporting Ukraine, Nato Secretary-General Jens Stoltenberg said.

“We see a Russian attempt to intimidate us from providing support, but we see that it has, if anything, the opposite effect on Nato allies,” he said. “They’re actually stepping up their support for Ukraine.”

German foreign minister Annalena Baerbock said Russia was “waging a hybrid war of aggression”.

“We have seen that there have been attacks on people on European territory, on factories,” Baerbock said in Washington, where she was attending the Nato summit.

“This underlines once again that we as Europeans must protect ourselves in the best possible way together.”

While the US learned about the specific Russian plot this spring, a German official said Papperger has had police security for more than a year.

The threat level at US bases was raised this month, after the Kremlin issued vague threats about consequences for Ukraine using US-made missiles to strike in occupied Crimea and at military bases in Russia. While related to the concerns about sabotage, the threat level was not connected to the plot against Papperger, according to the senior western intelligence official.

A spokesperson for Rheinmetall declined to comment.

Last year, Rheinmetall and a Ukrainian state-owned defence company set up a joint venture with the aim to begin building tanks and producing munitions in Ukraine.

The authorities in Moscow responded to the announcement of the plan by saying that such a factory would be a legitimate target, but Papperger, who has been strident in his support for Ukraine, insisted that would not stop him.

“We will not be dissuaded from our help for the country,” he told German newspaper Bild at the time.

New York Times News Service