WASHINGTON: Billionaire Elon Musk blasted President Donald Trump鈥檚 senior trade adviser Peter Navarro as 鈥渢ruly a moron鈥� and 鈥渄umber than a sack of bricks鈥� on Tuesday in a growing rift over the US tariff policy that has rocked the world.

The extraordinary public spat came after Navarro described the Tesla boss and so-called Department of Government Efficiency (DOGE) chief as 鈥渘ot a car manufacturer鈥� but 鈥渁 car assembler鈥� who relies on imported parts.

Musk, the world鈥檚 richest person, has previously signaled his opposition to the president鈥檚 new import tariffs that have roiled markets.

鈥淣avarro is truly a moron. What he says here is demonstrably false,鈥� Musk posted on his X social network, under a clip of Navarro saying Tesla imported batteries, electronics and tires, and that Musk 鈥渨ants the cheap foreign parts.鈥�

Musk doubled down in a series of other messages, saying that 鈥淭esla has the most American-made cars. Navarro is dumber than a sack of bricks.鈥�

Musk also dubbed him 鈥淧eter Retarrdo鈥� and said Navarro 鈥渟hould ask the fake expert he invented, Ron Vara鈥� 鈥� referring to a fictional pundit Navarro quoted in a series of books and a policy memo, using an anagram of his own name.

The South African-born tycoon recently backed the idea of a free-trade zone between North America and Europe 鈥� a wish at odds with Trump鈥檚 flagship tariffs.

The US president has ruled out any pause in his aggressive stance despite retaliatory action from China and signs of criticism from within his normally loyal Republican Party.

But there have also been conflicting messages from within the White House itself.

A long-time China hawk, Navarro has been one of the most hard-line voices on tariffs, and targeted Musk himself in an interview with CNBC.

鈥淲hen it comes to tariffs and trade, we all understand in the White House, and the American people understand, that Elon鈥檚 a car manufacturer. But he鈥檚 not a car manufacturer 鈥� he鈥檚 a car assembler in many cases,鈥� Navarro said.

鈥淚f you go to his Texas plant... the batteries come from Japan and from China, the electronics come from Taiwan.鈥�

The row came a day after Navarro insisted in an opinion piece in the Financial Times that the tariffs were 鈥渘ot a negotiation鈥� 鈥� only for Trump to admit later that he was in fact open to some negotiations.

The spat is all the more unusual because of the mesh of loyalties involved.

Trump has strongly defended Musk after a series of vandalism attacks and protests against Tesla over DOGE鈥檚 cost-cutting drive 鈥� even turning the White House into a pop-up showroom for the electric vehicles in a show of support.

Navarro, however, has proven his loyalty to Trump by serving a four-month jail sentence for contempt after refusing to testify to Congress on the January 6, 2021 attack on the US Capitol by Trump supporters.