DUESSELDORF/WASHINGTON ¨C Berlin is taking reports of a plot to assassinate the chief executive of arms manufacturer Rheinmetall very seriously and will not be cowed by Russian intimidation, the German government said on Friday.

A source familiar with the situation confirmed reporting by CNN and others that U.S. intelligence officials warned the German authorities this year that Russia was plotting to assassinate Armin Papperger, the head of Europe¡¯s biggest weapons producer, which has produced artillery shells and military vehicles for Ukraine.

A U.S. official, without confirming the report, said there has been an increased Russian efforts to conduct subversive or sabotage activities throughout Europe in the last five or six months.

These activities seemed to be targeting buildings, facilities, companies, and people involved in the supply of weapons to Ukraine, the official said.

The Rheinmetall plot was one of a series of Russian plans to assassinate defense industry executives across Europe supporting Ukraine¡¯s war effort, CNN reported. German security services were able to protect Papperger after Washington informed Germany, it said.

¡°We will not allow ourselves to be intimidated by Russia and will continue to do everything we can to prevent Russian threats in Germany,¡± Germany¡¯s Interior Minister Nancy Faeser said.

One of the world¡¯s biggest producers of artillery and tank shells, Rheinmetall has not directly confirmed the reports but said ¡°necessary measures are always taken¡± for security, in regular consultation with security authorities.

The Kremlin denied the reports as fake, based on anonymous sources, and said they could not be taken seriously.

An industry executive said the U.S. government had downplayed the threat inside the United States.

¡°We¡¯ve been in touch with intelligence agencies. They didn¡¯t believe there was any threat to U.S.-based CEOs,¡± the executive said.

In Washington, the White House declined to comment, but Adrienne Watson, a spokesperson for its National Security Council, said ¡°Russia¡¯s intensifying campaign of subversion is something that we are taking extremely seriously and have been intently focused on over the past few months.¡±

She said the U.S. has been discussing the issue with NATO allies, who met for a summit in Washington this week.

¡°We are actively working together to expose and disrupt these activities,¡± she said. ¡°We have also been clear that Russia¡¯s actions will not deter allies from continuing to support Ukraine.¡±

German defense group Hensoldt, which produces radar technology for the IRIS-T air defense system used in Ukraine, said it was reassessing safety measures.

The weapons division for Diehl, the German company that manufactures the IRIS-T and also produces ammunition, said it was monitoring the situation closely and would adapt its security measures if necessary.

BAE Systems has ¡°very rigorous security in place, which is kept under constant...