The United States foiled a Russian plot earlier this year to assassinate the chief executive of a major German arms maker supplying weaponry to Ukraine, CNN reported on Thursday.

The US cable television network, citing five unidentified US and Western officials, said the United States informed Germany of the Russian government's plan to kill Armin Papperger, the head of Rheinmetall, and he was given protection by German security services.

It said the assassination plot was one of a series of Russian plans discovered by US intelligence to kill European defense industry executives supporting Ukraine's war effort.

Rheinmetall produces 155mm artillery shells and plans to begin manufacturing armored vehicles in Ukraine, according to CNN.

The CNN report comes as NATO leaders are holding meetings in Washington to mark the 75th anniversary of the defense bloc.

German Foreign Minister Annalena Baerbock said: "In view of the latest reports on Rhinmetall, this is what we have actually been communicating more and more clearly in recent months.

"Russia is waging a hybrid war of aggression," Baerbock said. "With sabotage, with cyber attacks, with the paralysis of GPS so that Baltic aircraft can no longer land in neighbouring countries.

"We have seen that there have been attacks on people on European territory," the foreign minister said. "We have seen that there have been attacks on factories.

"And this emphasizes once again that we as Europeans must protect ourselves as best we can and not be naive."

A German interior ministry spokesman declined to comment directly on the Rheinmetall report but said the "German government takes the threats from the Russian regime very seriously.

"Our security authorities are very vigilant and act accordingly, in close cooperation with our international partners," the spokesman said. "We cannot comment on details, concrete protection measures and intelligence findings."

Rheinmetall spokesman Oliver Hoffmann said the company was "unable to comment on issues relating to corporate security."

"The necessary measures are always taken in regular consultation with security authorities," Hoffmann added.