President Donald Trump issued a rare threat of nuclear escalation on Friday, saying he had ordered two nuclear submarines to be strategically positioned near Russia in response to what he said were aggressive remarks by Dmitry Medvedev,

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.

The Kremlin said on Monday that everyone should be careful about nuclear rhetoric, in its first response to a statement by U.S. President Donald Trump that he had ordered a repositioning of U.S. nuclear submarines.