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.

"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 in a social media post that called Medvedev's statements highly provocative.

He said he ordered the submarines moved "just in case these foolish and inflammatory statements are more than just that. Words are very important, and can often lead to unintended consequences, I hope this will not be one of those instances."

Trump and Medvedev, who is deputy chairman of Russia's Security Council, traded taunts in recent days after Trump on Tuesday said Russia had "10 days from today" to agree to a ceasefire in Ukraine or be hit, along with its oil buyers, with tariffs.

Moscow, which has set out its own terms for peace in Ukraine, has shown no sign that it will comply with Trump's deadline.

Medvedev on Monday accused Trump of engaging in a "game of ultimatums" and reminded him that Russia possessed Soviet-era nuclear strike capabilities of last resort after Trump told Medvedev to "watch his words."

Medvedev has emerged as one of the Kremlin's most outspoken anti-Western hawks since Russia sent tens of thousands of troops into Ukraine in 2022. Kremlin critics deride him as an irresponsible loose cannon, though some Western diplomats say his statements illustrate the thinking in senior Kremlin policy-making circles.