Russia has delivered a formal diplomatic note to NATO warning that it would be prepared to use its entire arsenal, including nuclear weapons, if the alliance attempts to isolate the Kaliningrad region from the rest of Russia.

The non-paper, handed to the alliance on September 29, accused NATO of pursuing a “dangerous and reckless course” that carries “high risks of the outbreak of a direct armed conflict”. It warned that Russia would defend its territory “should NATO countries undertake any attempt aimed at isolating the Kaliningrad Region”, and raised the possibility of strikes against “decision-making centres” in alliance states.

NATO responded in writing, describing itself as a defensive alliance and urging Russia to end its invasion of Ukraine and cease “irresponsible nuclear rhetoric”. Alliance spokesperson Allison Hart said NATO strongly denounced the threat of force, while Secretary General Mark Rutte said he did not take the warning seriously, noting “Putin knows that he can never win (against) NATO.”

Russian embassies in London, Dublin and Brussels echoed the warning, claiming NATO was preparing an air and naval blockade of Kaliningrad — a claim made without public evidence.