Russia has issued a formal Kaliningrad nuclear warning to NATO, saying it would be ready to use nuclear weapons if alliance members try to isolate the Kaliningrad region from the rest of Russia, according to a diplomatic note seen by Reuters and reported on Sept. 30. NATO replied in writing that none of its exercises or activities threaten Russian territory, and told Moscow to stop its nuclear rhetoric. Neither document had been published in full when this was written.
What the Russian note says
The note, which Reuters reported was sent to NATO, says Russia would be ready to use the full range of its forces, including nuclear weapons, to defend its territory should NATO countries attempt to cut off Kaliningrad. It accuses the alliance of a “dangerous and reckless course” that carries high risks of direct armed conflict. Reuters also reported that the note raised the possibility of Russian strikes on decision-making centres in NATO states from the start of a conflict.
The message was not only private. Russian embassies in at least three European countries issued statements over the three days before the Reuters report, accusing NATO of raising tensions through exercises and planning scenarios involving Kaliningrad. Russia denies Western accusations that it is waging a hybrid war against Europe and rejects claims that it is preparing to attack a NATO country, according to Reuters and Politics Today.
How NATO responded to the Kaliningrad nuclear warning
NATO’s written reply, also seen by Reuters, described the alliance as defensive and said it counters threats to its members from every direction. It called on Russia to end its full-scale invasion of Ukraine and to stop what it described as irresponsible nuclear rhetoric. A NATO diplomat told Reuters the note confirms the alliance will not be deterred from supporting Ukraine.
Secretary General Mark Rutte repeated the message publicly. Asked whether a Russian nuclear attack on the Baltic states was now a real risk, Rutte said it was not, arguing that President Vladimir Putin understands Russia cannot defeat NATO, according to Politics Today.
The exchange came as the war in Ukraine, which NATO cited in its reply, kept escalating. The day after Reuters reported the note, Russian drones hit Kyiv’s Southern Bridge, the first such strike on the capital’s bridges since the full-scale invasion began, according to Meduza and the Kyiv Independent.
Why Kaliningrad is a flashpoint
Kaliningrad is a heavily militarized Russian exclave on the Baltic Sea, bordered by NATO members Poland and Lithuania and separated from the rest of Russia. That geography is why the Kaliningrad nuclear warning focuses on isolation: any attempt to cut the region’s links with the mainland would affect it directly. Reuters did not report what Moscow counts as an attempt to isolate the exclave.
A Western military source told Reuters that dozens of aircraft from NATO members took part in an unannounced operation in the airspace around Kaliningrad in mid-August. The source said it showed they could cut the exclave’s radio and radar links and its air defences in a conflict. That account could not be independently verified, and NATO’s reply says its activities pose no threat to Russia. Reuters reported that Moscow has voiced growing concern over NATO exercises around the region.
Reactions from Lithuania and Poland
An adviser to the Lithuanian president said the claims about Kaliningrad are unfounded and are being used to exert psychological pressure, according to Ukrainian outlets reporting on the Reuters story. Poland’s foreign minister, Radoslaw Sikorski, has called on NATO to step up military exercises near Kaliningrad, which lies between Poland and Lithuania.
How new is the threat
Nuclear warnings tied to the Baltic are not new. In April 2022, Dmitry Medvedev, deputy chairman of Russia’s Security Council, said there could be no talk of a nuclear-free Baltic if Sweden and Finland joined NATO. Lithuania’s defence minister replied then that nuclear weapons had long been kept in Kaliningrad, a claim by a Lithuanian official that HCN has not verified.
What stands out now is the form: a written diplomatic note delivered to the alliance. A senior European defence official told Reuters it was the first time since the Cold War that Russia had threatened NATO in this way and called it serious. That is an official’s assessment, not an established fact.
What is still unclear about the Kaliningrad nuclear warning
The wording of both documents comes from Reuters’ reporting, which other outlets then repeated, and HCN could not find the full texts. Neither side has described what an attempt to isolate the exclave would look like. It is also not established whether the note reflects a change in Russian nuclear policy or diplomatic pressure alongside the embassy statements. HCN found no Russian official comment beyond the note and those statements.
HCN will update its coverage of the Kaliningrad nuclear warning as more details of the exchange become public.