Former Russian President Dmitry Medvedev has issued a nuclear warning in the face of reports that Washington may authorize transferring US long-range Tomahawk missiles to Ukraine.

President Trump's latest remarks weighing in on the issue saw him veil his intentions in usually cryptic wording. Aboard Air Force One while traveling to the Middle East earlier Monday he had said Tomahawks are a "very offensive weapon," noting, "honestly, Russia does not need that."

Headlines throughout the say said he 'might' approve of sending them. These are missiles capable of hitting Moscow. This is also as last month Trump surprised observers by claiming that Ukraine could still 'win' the war and actually regain territory.

Medvedev's chilling response on Monday spelled out that this "could end badly for everyone … most of all, for Trump himself," according to a translation of his Telegram post.

"It's been said a hundred times, in a manner understandable even to the star-spangled man, that it's impossible to distinguish a nuclear Tomahawk missile from a conventional one in flight," Medvedev, who serves as the Russian Security Council Deputy Chair, further noted.

Medvedev here is alluding to Russian strategic doctrine. In a scenario where Moscow leaders believed or suspected a nuclear payload had been launched at Russia, its military would have the right to respond in kind, with nukes.

The past couple months have seen Trump and Medvedev direct threatening messages at each other, particularly related to Trump proclaiming that he had deployed a pair of nuclear submarines somewhere near Russia.

Thankfully it has all so far been confined to social media barbs, and not any clear instance of either side's strategic forces being placed on emergency alert.

But Medvedev's latest message is meant as a clear 'red line' warning to Washington - that things could rapidly and uncontrollably escalate in Ukraine if the US sends Tomahawk missiles to use against Russia.

President Zelensky has meanwhile sought to make clear he won't target anything but military sites with them, in an effort to convince Washington these long-range missiles can be deployed 'responsibly'.