Russia has threatened to deploy nuclear weapons and hypersonic missiles if Sweden and Finland join NATO.
The two countries have suggested they could join the North Atlantic Treaty Organisation in the wake of Russia invading Ukraine and launching an all-out war in the region.
However, a spokesperson within Russia's government has strongly urged the Nordic nations to back down or else they will be forced to escalate their protection measures.
Chairman of Russia's Security Council, Dmitry Medvedev, said the Kremlin will not be intimidated by Sweden and Finland.
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"There can be no more talk of any nuclear-free status for the Baltic - the balance must be restored," he said, according to Sky News.
"Until today, Russia has not taken such measures and was not going to."
Finland and Sweden will make a decision in the coming weeks on whether to join NATO, however a poll within the two countries suggests many people support the move.
Finland shares a 1,300km border with Russia and joining the organisation will be a massive step.
Medvedev says they would strategically move their weapons arsenal to Kaliningrad, which is a small enclave sandwiched between Poland and Lithuania.
"No sane person wants higher prices and higher taxes, increased tensions along borders, Iskanders, hypersonics and ships with nuclear weapons literally at arm's length from their own home," the former Russian President said.
"Let's hope that the common sense of our northern neighbours will win."
However, Lithuania says the Russian threat of nuclear escalation has been around for a while now.
The country's Defence Minister called Medvedev's bluff.
Arvydas Anusauskas was quoted by BNS as saying: "Nuclear weapons have always been kept in Kaliningrad...the international community, the countries in the region, are perfectly aware of this.
"They use it as a threat.
"The current Russian threats look quite strange when we know that, even without the present security situation, they keep the weapon 100km from Lithuania's border."
Lithuania's Prime Minister added that Russia always likes to flex this nuclear muscle whenever it feels particularly threatened.
Sweden and Finland say their security situation has changed since Russia's invasion of Ukraine and they want to ensure their citizens feel safe.
They will be acting quickly over the next few weeks to see whether joining is the right step for everyone and it will be very interesting to see what happens in Russia if and when they decide.
Stewart Perrie