Moscow has sent NATO a formal diplomatic warning this week, demanding that the alliance abandon any plan to isolate Kaliningrad, the heavily militarised Russian exclave squeezed between Poland and Lithuania on the Baltic Sea. The note, confirmed by officials in Brussels, marks one of the sharpest exchanges between Russia and NATO since the war in Ukraine began, and it has reignited fears that a small territory of barely 400,000 people could become the flashpoint for a much larger confrontation. Kaliningrad, once the German city of Königsberg, has long been a strategic headache for European planners. It hosts Russia's Baltic Fleet and is believed to store nuclear-capable Iskander missiles, yet it depends on road and rail links through Lithuania, a NATO member, for much of its supplies.

Any disruption to that corridor, Moscow argues, would be treated as an act of hostility. NATO officials, for their part, insist they have no intention of sealing off the enclave, but they accuse the Kremlin of exaggerating the threat to justify its own posture. "Russia is using irresponsible nuclear rhetoric to intimidate its neighbours," a NATO spokesperson said, in a statement that has been echoed across capitals from Warsaw to Washington. Lithuanian officials, who briefly restricted the transit of sanctioned goods to Kaliningrad in 2022 before easing the measure under EU pressure, say they are merely enforcing sanctions rules, not besieging Russian territory.

The dispute lands at a delicate moment, as NATO members debate further troop deployments in the Baltic states and Russia continues to reinforce its western military districts. Analysts in Berlin and Helsinki warn that even a minor miscalculation around Kaliningrad's supply lines could trigger a crisis neither side says it wants.