Russia has threatened serious but undisclosed measures against Lithuania over the NATO member’s rail blockade of its exclave Kaliningrad.

Russian Security Council chief Nikolai Patrushev said Tuesday that the move will carry “serious negative consequences” for the Baltic country’s citizens. European Union member Lithuania banned the rail transit of sanctioned Russian goods through its territory on Saturday.

This has sparked outrage in Moscow as well as a wave of panic-buying in its exclave region surrounded by EU and NATO member states. 

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This is the first time Russia has issued a direct warning to a NATO member since the beginning of the war in Ukraine.

“Russia will, of course, respond to hostile actions of this kind,” Patrushev, a close adviser of Russian President Vladimir Putin, said at a security meeting in the Kaliningrad region’s capital of the same name. 

“The necessary measures […] will be introduced shortly. They will have serious negative consequences for residents of Lithuania.” 

Kaliningrad is a strategic region where Russia’s Baltic Fleet is headquartered. This has no border with mainland Russia. The region relies heavily on rail transit via Lithuania.

Patrushev condemned Lithuania’s move as “orchestrated by the West against norms and principles of international law.” He said the ban demonstrated that Russia cannot trust “neither verbal nor written promises made by the West.”

Patrushev’s comments came as Russia’s Foreign Ministry summoned the EU’s ambassador to Moscow to discuss the latest tensions in the Baltics.

During the meeting, Russian diplomats voiced their “strong protest” against “unilateral anti-Russia restrictions” imposed by Lithuania. However, EU Ambassador Markus Ederer stressed that a total blockade was “out of the question.”

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“Transit for people and goods not affected by sanctions is operating as normal,” the state-run TASS news agency quoted Ederer as saying after the meeting.

“I have asked the Russian side to keep calm and not escalate [the situation] verbally or action-wise and resolve the question diplomatically.”