Russia has sent a closed message to NATO through diplomatic channels, warning that it is ready to use nuclear weapons if the alliance tries to take the Kaliningrad region under siege, Reuters reports. In the document under the agency's control, Moscow accuses the bloc of "irresponsible policy" that "contains a serious risk of conflict". At the same time, the Russian side emphasizes that in the event of a military conflict, it will immediately strike "the decision-making centers of the member countries of the alliance". "This is the first time since the Cold War that Russia has sent such a threat to us, so this should be taken seriously," a high-ranking official of the defense department of one of the European countries told Reuters. The NATO source, in turn, described this as "another attempt to terrorize the Europeans", adding that the reaction will be "decisive" and the alliance will not stop providing support to Ukraine. NATO press secretary Alison Hart confirmed the fact of receiving the Russian note. "In our response note, we emphasized that NATO is a defense alliance, and our steps and military exercises do not pose any threat to Russia. We strongly condemn threats of force and irresponsible nuclear rhetoric," Hart said. After sending the document to the NATO headquarters, Russian embassies in European countries publicly accused the alliance of inciting tension around Kaliningrad. The announcements state that Moscow is not going to attack NATO, but warns that any aggression against Kaliningrad will be met with the harshest response.