Dmitry Medvedev, the former Russian president, said on Thursday that it would be impossible for the Baltic region to remain “non-nuclear” if Sweden and Finland joined the NATO alliance, writes The Financial Times.

“If Sweden and Finland join NATO, the length of the alliance’s land borders with Russia will more than double”, - Medvedev, now deputy chair of Russia’s Security Council, wrote on his personal channel on the Telegram messaging app. “Naturally, these borders will have to be strengthened”.

“If this is done, no non-nuclear status of the Baltic will be possible”, Medvedev said. “The balance must be restored”. The people of Sweden and Finland, he added, would end up with nuclear-armed Russian ships “at arm’s length” from their homes.

His comments are some of the toughest yet from a prominent Russian figure about the Kremlin’s potential reaction to a NATO application from the two Nordic countries.

Finland’s Prime Minister Sanna Marin said on Wednesday the country would decide within “weeks” whether to apply to join NATO. Sweden has also edged closer to seeking membership in the wake of Russia’s invasion of Ukraine.

Medvedev said ground and air defence forces would have to be “seriously reinforced” and “considerable naval forces” would need to be deployed in the Gulf of Finland if the two countries joined NATO,

He said public opinion on the issue was divided in the Nordic nations and that “no sane person” would want the consequences of this move - “increased tensions along the borders, Iskanders, hypersonic weapons, and nuclear-armed ships literally at arm’s length from their own homes”.