The U.S. and Germany claimed to have foiled a Russian plot to assassinate Armin Papperger, the CEO of Rheinmetall, a German arms manufacturer that supplies Ukraine with artillery shells, tanks and other weapons, according to five sources close to the situation who spoke to CNN. As leaders gathered in Washington, D.C. for the 75th NATO summit, CNN reported that Russia has been attempting to kill Papperger, along with other executives of European defense companies. Rheinmetall is the main supplier of 155 mm artillery shells to Ukraine, recently signing a contract with the German government to buy $6.5 billion worth of shells to be supplied to Ukraine, according to CNN. The company is also opening a factory in Ukraine that will produce and repair tanks within the coming weeks, according to CNN. “We have seen that there have been attacks on factories. And this underlines once again that we as Europeans must protect ourselves as best we can and not be naive,” Germany’s Foreign Minister Annalena Baerbock told CNN outside the NATO summit Thursday. “The necessary measures are always taken in regular consultation with the security authorities,” a spokesman for Rheinmetall, Oliver Hoffman, told CNN. The Russian embassy in D.C. did not return CNN’s request for comment.