The US president said he's ordered two nuclear submarines to move closer to Russia, after a social media spat with Russia's ex-president.

Donald Trump has revealed that two US nuclear submarines are now positioned "closer to Russia" following a tense exchange with former Russian president Dmitry Medvedev.The submarines were initially said to be deployed to "appropriate regions" in what was widely seen as a symbolic gesture.

"I have ordered two Nuclear Submarines to be positioned in the appropriate regions, just in case these foolish and inflammatory statements are more than just that," Trump said. US President Donald Trump on Friday said he had ordered two nuclear submarines to be positioned in regions near Russia in response to threats from former Russian president Dmitry Medvedev.