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.

Medvedev on Monday harshly criticized Trump's threat of new sanctions against Russia over the continuing invasion of Ukraine.

"I have ordered two Nuclear Submarines to be positioned in the appropriate regions, just in case these foolish and inflammatory statements are more than just that," Trump said. US President Donald Trump on Friday said he had ordered two nuclear submarines to be positioned in regions near Russia in response to threats from former Russian president Dmitry Medvedev.