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.

Trump also rebuked Medvedev in July, accusing him of throwing around the "N (nuclear) word" after the Russian official criticised U.S. strikes on Iran and said "a number of countries" were ready to supply Iran with nuclear warheads.

Dmitry Medvedev said President Trump is "playing the ultimatum game with Russia" in pressuring for an end to the war on Ukraine.