Washington DC - President Donald Trump expressed interest Friday in an undersea tunnel connecting the state of Alaska with Russia – a project floated a day earlier by a senior Russian official to billionaire Elon Musk.

"A tunnel from Russia to Alaska. That's... interesting," Trump said, when asked about the idea by White House reporters during his meeting with Ukrainian counterpart Volodymyr Zelensky.

Indicating he had just heard about the potential cross-border project, he asked Zelensky: "What do you think of that, Mr. President?... How do you like that idea?"

The Ukrainian leader – who has been combating a full-scale Russian invasion for over three years – appeared less than thrilled.

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"I'm not happy with this," he said, eliciting a laugh from his host.

Russian President Vladimir Putin's international economy envoy, Kirill Dmitriev, brought up the idea on Thursday on the Musk-owned media platform X.

He claimed the idea of a "peace bridge" between Russia and Alaska dated back to the Cold War era, and posted a crude graphic showing a proposed tunnel route under the Bering Sea.

"With modern @boringcompany technology this can become a Putin-Trump tunnel," a 70-mile link connecting Russia to the Americas for under $8 billion, Dmitriev posted.

The Boring Company is yet another venture by Musk, the world's richest person and boss of Tesla and SpaceX, which aims to revolutionize urban transport through the construction of tunnels.

Dmitriev, who heads Russia's sovereign wealth fund, said Musk's company could build the tunnel – a project "symbolizing unity" – in under eight years.

Musk was one of the biggest donors to Trump's 2024 campaign. After Trump returned to the White House, Musk joined the Republican's administration, with the president tasking him with making dramatic cuts to the federal budget, including laying off thousands of government employees.

Trump and Musk were close until the latter left the administration in May. They publicly fell out in June, with Musk launching fierce attacks over Trump's economic policies.

The two nevertheless appeared side by side on September 21 during a ceremony honoring slain far-right influencer Charlie Kirk.