SpaceX founder Elon Musk on Monday took to Twitter to challenge Russian President Vladimir Putin to a one-on-one fight – with war-torn Ukraine's fate as the prize.

The eccentric billionaire and world's richest man known for his notorious tweets posted the offer on his Twitter account to see whether the Russian leader would test his mettle in person rather than through his country's forces fighting across the border.

"I hereby challenge Vladimir Putin to single combat. Stakes are Ukraine," Musk said.

"Do you accept this fight?" he added in Russian, directly addressing the official English-language Twitter account of the 69-year-old president.

When one of Musk's 77 million followers wrote that the Tesla founder might not have thought his challenge through, Musk said he was "absolutely serious."

"If Putin could so easily humiliate the West, then he would accept the challenge. But he will not," he added.

There was no immediate reaction from the Kremlin.

The South African-born Musk, 50, had already offered his support for Kyiv, tweeting "Hold strong Ukraine" this month while also offering "my sympathies to the great people of Russia, who do not want this" war.

He also responded to a Kyiv plea by activating the Starlink internet service in Ukraine and sending equipment to help bring connectivity to areas hit by Russian military attacks.

Musk often raises eyebrows on Twitter. In February, he accused the United States stock market regulator, which had imposed fines and restrictions on Musk and Tesla, of trying to muzzle his free speech.

And he compared Canadian Prime Minister Justin Trudeau to Adolf Hitler in a message supporting opponents of government COVID-19 restrictions. However, he later deleted the post.