One of Russian President Vladimir Putin’s closest allies warned NATO on Thursday that if Sweden and Finland joined the US-led military alliance then Russia would deploy nuclear weapons and hypersonic missiles in an exclave in the heart of Europe.

Finland, which shares a 1,300km (810-mile) border with Russia, and Sweden are considering joining the NATO alliance.

Dmitry Medvedev, deputy chairman of Russia’s Security Council, said that, should Sweden and Finland join NATO, then Russia would have to strengthen its land, naval and air forces in the Baltic Sea.