US President Donald Trump said Friday he was ordering two US Navy nuclear submarines to positions closer to Russia, in response to remarks by Dmitry Medvedev, Russia’s former president and current deputy chairman of its Security Council.

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, the country’s former president and current deputy chairman of its Security Council.

The move follows comments by former Russian president Dmitry Medvedev reminding President Donald Trump that Moscow possesses nuclear strike capabilities.