Kirill Dmitriev first posted about the idea on Thursday, suggesting a “Putin-Trump” rail tunnel could connect the two countries under the Bering Strait, which separates Russia’s vast and sparsely populated Chukotka region from Alaska.
Asked about the idea during a press conference with Ukraine’s President Volodymyr Zelenskyy on Friday, Donald Trump called it “interesting”.
He also asked President Zelenskyy what he made of it, to which Mr Zelenskyy replied: “I’m not happy with this idea.”
This prompted laughter from the US side.
Overnight, Mr Dmitriev posted on X, saying: "We have started the feasibility study of the Russia-Alaska tunnel six months ago.
This would be the most ambitious engineering feat in human history. A project to rival colonization of Mars in expense and danger. All to connect one wilderness to another. Brilliant.