The Kremlin has tried to calm tensions in a feud between Trump and Medvedev that spiraled into nuclear threats.

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.

Russia said on Monday that everyone should be "very, very careful" about nuclear rhetoric, responding to a statement by U.S. President Donald Trump that he had ordered a repositioning of U.S. nuclear submarines.