US President Donald Trump says he has ordered two nuclear submarines to "be positioned in the appropriate regions" in response to "highly provocative" comments by former Russian President Dmitry Medvedev.

It comes amid heightened tensions over Russia’s invasion of Ukraine, after Trump described Russia’s actions as “disgusting”. The US President had given Putin a 50-day deadline to end the war, which he then reduced to less than two weeks following an unsatisfactory response from the Russian president.

It comes after Dmitry Medvedev, who is now deputy chair of Russia's Security Council, told the US president to remember Moscow had Soviet-era nuclear strike capabilities of last resort.