Donald Trump has said that he has deployed nuclear-capable submarines to the “appropriate regions” in response to a threatening tweet by Russia’s former president Dmitry Medvedev, suggesting that he would be ready to launch a nuclear strike as tensions rise over the war in Ukraine.

In a post on Truth Social on Friday, Trump wrote that he had decided to reposition the nuclear submarines because of “highly provocative statements” by Medvedev, noting he was now the deputy chairman of Russia’s security council.

Medvedev had earlier said that Trump’s threats to sanction Russia and a recent ultimatum were “a threat and a step towards war”.

“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 responded. “Words are very important, and can often lead to unintended consequences, I hope this will not be one of those instances.”

He did not specify whether he was referring to nuclear-powered or nuclear-armed submarines.

Asked later by reporters why he ordered the submarine movement, Trump said: “A threat was made by a former president of Russia and we’re going to protect our people.”