Russia's investment envoy has said research into the feasibility of a tunnel joining the US and Russia started "six months ago".

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.

"Russian Direct Investment Fund with partners financed on a commercial basis the first ever railroad bridge between Russia and China.

"The bridge reduced cargo route by more than 700 kilometres," he said.

He directed a post on X towards Elon Musk, suggesting the tunnel could be dug by the billionaire's construction firm, Boring Company.

"The dream of a US-Russia link via the Bering Strait reflects an enduring vision - from the 1904 Siberia-Alaska railway to Russia's 2007 plan," Mr Dmitriev wrote.

"RDIF has studied existing proposals, including the US-Canada-Russia-China railroad, and will support the most viable.

"Imagine connecting the US and Russia, the Americas and the Afro-Eurasia with the Putin-Trump Tunnel - a 70-mile link symbolizing unity."

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"Traditional costs are $65B+, but @boringcompany's tech could reduce it to future together," he added.

There has been no public response from Elon Musk.

(c) Sky News 2025: Donald Trump responds to idea of tunnel connecting Russia and US