Elon Musk has called President Donald Trump's trade adviser, Peter Navarro, a "moron" over comments he made about his electric vehicle firm, Tesla.
Musk - who is also a member of the Trump administration - also said Navarro was "dumber than a sack of bricks" in posts on his social media platform X.
It was in response to an interview Navarro gave in which he described Tesla as a "car assembler", rather than a manufacturer, because of its use of foreign-made parts.
Navarro was being interviewed about Trump's tariff policy and said he wanted to see such parts made in the US in the future instead.
Musk said the claims were "demonstrably false."
The BBC has asked the White House for comment.
Trump has in part justified his global wave of tariffs by saying he wants to revive manufacturing in the US.
This is an argument Navarro was expanding on during an appearance on CNBC on Monday.
"If you look at our auto industry, right, we're in assembly line for German engines and transmissions right now", he said.
"We're going to get to a place where America makes stuff again, real wages are going to be up, profits are going to be up".
Responding to the comments on Tuesday, Musk posted a link to a 2023 article by car valuation firm Kelley Blue Book, which cited Car.com findings that Tesla vehicles had the most parts produced in the US.
"By any definition whatsoever, Tesla is the most vertically integrated auto manufacturer in America with the highest percentage of US content," Musk wrote in a follow-up post.
Technology industry analyst Dan Ives said on Sunday that the company was less exposed to tariffs than other US car makers such as GM, Ford, and Stellantis.
But he too claimed the company sourced the majority of its parts from outside the US, highlighting China.
"The tariffs in their current form will disrupt Tesla, the overall supply chain, and its global footprint which has been a clear advantage over the years vs. rising competitors like BYD," he said.
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Trump's tariffs have caused stock market falls around the world, as investors calculate it will result in firms making smaller profits.
Musk - who is leading DOGE, which is tasked with cutting federal spending - warned in an X post on 27 March that even his company would not be immune from tariff disruption.
Another Trump backer, the billionaire fund manager Bill Ackman, has called for a pause on the tariffs to stave off what he called "major global economic disruption."
In a post on X, he said the current plans would do "unnecessary harm."
Navarro is considered an ultra-Trump loyalist after being jailed for ignoring a subpoena from a House committee investigating alleged efforts to overturn the 2020 election.
He is also thought to be one of the main architects of Trump's tariff policy.