Moscow threatens nuclear response over tiny fortress wedged between US allies as clash fears grow

Russia’s warning that it could resort to nuclear weapons if NATO attempts to isolate Kaliningrad is raising new concerns that the heavily militarized Russian exclave could become a flashpoint between Moscow and the alliance, as experts warn the territory is already being used to pressure Europe through hybrid warfare.

Moscow warned NATO in a diplomatic document that it was prepared to use “the entire arsenal of forces and capabilities at its disposal, including nuclear weapons” if alliance members attempted to isolate Kaliningrad from the rest of Russia, Reuters reported Wednesday.

Kaliningrad, a Russian territory geographically separated from the Russian mainland, sits...