The Kremlin on Monday called Lithuania's decision to ban the transit of some goods to Russia's Kaliningrad region "unprecedented" and vowed to respond.
Lithuanian authorities banned the transit of goods which are sanctioned by the European Union across its territory, which includes the only rail route between mainland Russia and the Kaliningrad exclave on the Baltic Sea. Banned goods include coal, metals, construction materials and advanced technology.
"This decision is really unprecedented. It's a violation of everything," Kremlin spokesperson Dmitry Peskov said in a call with reporters on Monday.
"We consider this illegal. The situation is more than serious ... we need a serious in-depth analysis in order to work out our response," he added.
Sandwiched between EU and NATO members Poland and Lithuania, Kaliningrad receives supplies from Russia via rail and gas pipelines through Lithuania.
Kaliningrad's governor estimated the ban could affect up to half of all goods that are brought to the region by rail.