US President Donald Trump last night confirmed that two US Navy nuclear submarines are 'getting closer to Russia', dramatically escalating tensions between the two countries.

Mr Trump ordered the submarines, packed with nuclear warheads, towards Russian waters after an online spat with former Russian president Dmitry Medvedev – now deputy chairman of Russia's National Security Council – who said: 'Each new ultimatum is a threat and a step towards war.'

The sabre-rattling came after Mr Medvedev wrote on social media platform Telegram that Russia could invoke 'Dead Hand' – a doomsday program with the ability to automatically launch a nuclear counterstrike against major US cities, even if Moscow and President Vladimir Putin are wiped out.

Mr Medvedev wrote: 'As for the talk about the 'dead economies' of India and Russia, and 'entering dangerous territory' – maybe he should recall his favourite movies about 'the walking dead,' and also remember how dangerous the so-called 'Dead Hand', that does not exist in nature, could be.

'He should remember two things: 1: Russia isn't Israel or even Iran. 2: Each new ultimatum is a threat and a step towards war. Not between Russia and Ukraine, but with his own country. Don't go down the Sleepy Joe [a reference to former President Joe Biden] road!'