Medvedev said Russia would deploy "significant naval forces" in the Gulf of Finland if the country joined NATO.
ADVERTISEMENTThe deputy chair of Russia's security council has said the country would have to reinforce its forces in the Baltic Sea if Finland or Sweden were to join the North Atlantic Treaty Organisation (NATO).
Dmitry Medvedev wrote in a Telegram post on Thursday that if the countries joined the Western military alliance, there would not be any "nuclear-free status of the Baltic".
The former Russian president and prime minister said that it would mean more ground forces and air defence, as well as deploying "significant naval forces" in the Gulf of Finland.
He said that Finland or Sweden joining NATO would mean the "length of the alliance's land borders with Russia will more than double".
"Naturally, these borders will have to be strengthened," he added.
Lithuanian defence minister Arvydas Anušauskas was quoted by the Baltic News Service as saying the threats were "strange" because there are already nuclear weapons in the Kaliningrad region.
While both Finland and Sweden had previously shied away from joining the alliance, the war in Ukraine has changed the conversation. Finland shares a 1,340-kilometre-long land border with Russia.
Finnish Prime Minister Sanna Martin said the country would decide on whether to apply for NATO membership in "weeks rather than months", stating that the war in Ukraine had changed "everything".
Meanwhile, Medvedev implied that discussions of Finland and Sweden joining NATO would have been raised even if Russia had not invaded Ukraine.
"Attempts to drag them into the alliance have been made before," he said.
He said that "no sane person" would want increased border tensions and nuclear-powered ships near their homes.