Former Russian president Dmitry Medvedev has become embroiled in a tense back-and-forth on social media that prompted U.S. President Donald Trump to announce he had ordered the re-positioning of two U.

President Donald Trump has ordered the repositioning of two U.S. nuclear submarines. Friday's decision comes after what he calls "highly provocative statements" by former Russian President Dmitry Medvedev.

Kremlin spokesperson Dmitry Peskov has urged President Donald Trump to exercise caution when uttering what the Kremlin called "nuclear rhetoric" after Trump and former Russian President Dmitry Medvedev had a heated exchange.