The Russian Foreign Ministry demanded Lithuania lift a partial blockade of Kaliningrad, the Russian region located near the Baltic Sea, and warned that such an action is "openly hostile."
Kaliningrad, formerly known as Konigsberg, is located between NATO members Poland and Lithuania, although it has been Russian territory for the past 70 years or so.
Last week, Lithuania announced that it was banning the rail transit of goods and supplies to Kaliningrad that are subject to European Union sanctions. That includes coal, construction materials, metals, and advanced technology.
On Monday, the Russian Foreign Ministry described the blockade as "provocative measures" and warned that the Kremlin might take action to protect its interests.
The ministry said it summoned a Lithuanian diplomatic official to Moscow to protest the Baltic country's recent measures. The blockade, it said, violates a 2002 Russia–EU agreement.
Details of the blockade came on June 17 through a video posted by the Russian region's governor, Anton Alikhanov. He told residents not to panic buy and said two ships were on the way to transport goods to Kaliningrad, according to Reuters.
"Our ferries will handle all the cargo," Alikhanov said Saturday.
Lithuanian Deputy Foreign Minister Mantas Adomenas, meanwhile, told a public broadcaster his institution was waiting for "clarification from the European Commission on applying European sanctions to Kaliningrad cargo transit."
Lithuania said it was merely implementing EU sanctions, part of a swathe of measures intended to punish President Vladimir Putin for the invasion of Ukraine.
"It's not Lithuania doing anything: it's European sanctions that started working from 17 of June," Lithuanian Foreign Minister Gabrielius Landsbergis told reporters in Luxembourg.
"It was done with consultation from European Commission and under European Commission guidelines," Landsbergis continued to say.
The sanctions and Kaliningrad blockade come as the Russia–Ukraine conflict continues to rage, namely in the eastern part of Ukraine. The EU, United States, and several other Western nations have issued harsh sanctions against Russia since the start of the Feb. 24 conflict, including a U.S. ban on all Russian oil.