Musk responded to a tweet from a pro-Kremlin Twitter account early on Monday that claimed that 157,000 Ukrainian soldiers had been killed since February, along with 234 US and British Nato military trainers and thousands of Nato soldiers.
“A tragic loss of life,” Musk wrote, in a post that received nearly 11 million impressions in just over 12 hours.
The post from the @RuNews Twitter account, which linked to a little-known Turkish language news site, was quickly debunked. Nato member countries including the US and Britain have supplied weapons, money and logistical support, but have decided against sending in troops.
Musk, who has a history of making dubious claims about the war that have been interpreted as being pro-Russian, was heavily criticised.
“You literally own one of the biggest social media companies and you are spreading this absolute misinformation,” former Congressman Adam Kinzinger tweeted.
“Elon is really an agent of misinfo or he is so desperate for approval he picks the alt right.”
Turkish journalist Ilhan Tanir wrote in response that he had never heard of the news site that Musk was relying on, and pointed out there was no source or attribution for the figures it quoted, other than to say the numbers had come from the Israeli intelligence service the Mossad.
“Even my aunt would be more careful,” Mr Tanir tweeted. “What r u doing? @elonmusk. Embarrassing.”
Author and journalist Michael Weiss pointed out that after Musk had fallen for the easily disprovable claim that thousands of Nato soldiers and military trainers had been killed in fighting, the same pro-Kremlin account invited him to play peacemaker.
“Elon Musk, evidently very concerned about media corruption and fake news, takes the bait, then is asked by the account to ‘mediate.’”
After his tweet came in for criticism, Musk asked “Community Notes”, a crowdsourced factchecking system on Twitter, to correct the figures.
A supplemental post was added to show that General Mark Milley, the US’s top ranking military officer, put the total number of Ukrainian soldiers killed in the fighting at about 100,000 in November.
It also linked to an article on the BBC debunking Russian claims that Nato soldiers or military trainers were operating in the country.
Musk has previously argued against sending tanks to help the Ukrainian forces, which military leaders say are vital to the continued defence of the country.
“Tanks are a deathtrap now,” Musk tweeted in January. “With neither side having air superiority, you’re left with infantry & artillery – essentially WW1.”
In October, he issued an unsolicited peace plan that called for elections in Russian-occupied parts of eastern Ukraine and for Crimea to be recognised as part of Russia.
He also claimed that “civilization is over” if Ukraine doesn’t give in to Russia’s demands.
Prominent Russia expert Fiona Hill said Musk appeared to be “transmitting a message” for Vladimir Putin in an interview with Politico.