Former Russian President Dmitry Medvedev, one of Vladimir Putin’s closest advisers, warned that Russia would arm nukes in the Baltic region if Finland and Sweden joined NATO.

The threat came after Finnish politicians hinted at the growing likelihood that the country would join the alliance. Finland shares the longest land border with Russia of any country in Europe at 810 miles.

Medvedev, the current deputy chairman of the Russian Security Council, said that should the two Nordic countries decide to join the United States-led alliance, it will force Russia to bolster its land, naval, and aerial capabilities in the region.

“If Sweden and Finland join NATO, the length of the land borders of the alliance with the Russian Federation will more than double. Naturally, these boundaries will have to be strengthened,” he wrote on Telegram.