Russian authorities Monday threatened Lithuania, a member of NATO, with retaliation if the Baltic country does not swiftly reverse its ban on the transportation of some goods to Russia’s exclave of Kaliningrad by rail.

Citing instructions from the European Union, Lithuania’s railway Friday said it was halting the movement of goods from Russia that have been sanctioned by the European bloc.

Dmitry Peskov, the Kremlin’s spokesman, told reporters the situation was “more than serious.” He called the new restrictions “an element of a blockade” of the region and a “violation of everything.”

Accustomed to Russian threats, officials in Vilnius, the Lithuanian capital, took Moscow’s warnings as mostly bluster — the latest in a series of increasingly intemperate statements by a country that is severely stretched militarily by its invasion of Ukraine.

“We are not particularly worried about Russian threats,” said Lauynas Kasciunas, chair of the Lithuanian Parliament’s national security and defense committee. “The Kremlin has very few options for how to retaliate.”

A military response by Russia, he added, “is highly unlikely because Lithuania is a member of NATO. If this were not the case, they probably would consider it.”

Russia’s fury at Lithuania followed a warning earlier Monday by Ukrainian President Volodymyr Zelenskyy that Moscow would initiate “greater hostile activity” against Ukraine and European countries in the coming days in response to his nation’s efforts to join the European Union.

Up to 50% of all rail cargo shipped between mainland Russia and Kaliningrad — which Russian officials said includes construction materials, concrete and metals among other items — will be affected by the ban announced last week. The restrictions exposed the acute vulnerability of the region, which is part of Russia but not connected to the rest of the country. It borders the Baltic Sea but is sandwiched between two NATO members, Lithuania and Poland.

Kaliningrad, which the Soviet army seized from Germany in 1945, was once touted by Russia as a symbol of its growing ties with Europe. But it has lately become a volatile East-West fault line.

Gripped by increasingly aggressive nationalism, Russia has ditched policies that promoted Russia as part of Europe and moved advanced Iskander missiles into Kaliningrad. Lithuania’s defense minister said in April that Russia has stationed nuclear weapons in the region, which Moscow denies.