US President Donald Trump (L) and Tesla and SpaceX CEO Elon Musk watch a fight during UFC 309 at Madison Square Garden in New York, on November 16, 2024. Kena Betancur, AFP/File

WASHINGTON -- Billionaire Elon Musk has criticized Donald Trump's signature spending bill, in his first major break with the US president since he stepped back from his role taking a chainsaw to government spending.

The South African-born tech tycoon said Trump's bill would increase the deficit and undermine the work of Musk's Department of Government Efficiency (DOGE), which has fired tens of thousands of people.

Musk -- who was a constant presence at Trump's side before pulling back to focus on his Space X and Tesla businesses -- also complained that DOGE had become a "whipping boy" for dissatisfaction with the administration.

"I was disappointed to see the massive spending bill, frankly, which increases the budget deficit, not just decreases it, and undermines the work that the DOGE team is doing," Musk said in an interview with CBS News, an excerpt of which aired late Tuesday.

Trump's "One Big, Beautiful Bill Act" -- which passed the US House last week and now moves to the Senate -- offers sprawling tax relief and spending cuts and is the centerpiece of his domestic agenda.

But critics warn it will decimate health care and balloon the national deficit by as much as $4 trillion over a decade.

"A bill can be big, or it can be beautiful. But I don't know if it can be both. My personal opinion," Musk said in the interview, which will be aired in full on Sunday.

The White House sought to play down any differences over US government spending, without directly naming Musk.

"The Big Beautiful Bill is NOT an annual budget bill," Trump's Deputy Chief of Staff Stephen Miller said on Musk's social network, X, after the tech titan's comments aired.

All DOGE cuts would have to be carried out through a separate bill targeting the federal bureaucracy, according to US Senate rules, Miller added.

But Musk's comments represented a rare split with the Republican president whom he helped propel back to power, as the largest donor to his 2024 election campaign.

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- 'Whipping boy' -

Trump tasked Musk with cutting government spending as head of DOGE, but after a feverish start Musk announced in late April he was mostly stepping back to run his companies again.

Musk complained in a separate interview with the Washington Post that DOGE, which operated out of the White House with a staff of young technicians, had become a lightning rod for criticism.

"DOGE is just becoming the whipping boy for everything," Musk told the newspaper at the Starbase launch site in Texas ahead of Space X's latest launch on Tuesday.

"Something bad would happen anywhere, and we would get blamed for it even if we had nothing to do with it."

Musk blamed entrenched US bureaucracy for DOGE's failure to achieve all of its goals -- although reports say his domineering style and lack of familiarity with the currents of Washington politics were also major factors.

"The federal bureaucracy situation is much worse than I realized," he said. "I thought there were problems, but it sure is an uphill battle trying to improve things in DC, to say the least."

Musk has previously admitted that he did not achieve all his goals with DOGE even though tens of thousands of people were removed from government payrolls and several departments were gutted or shut down.

Musk's own businesses suffered in the meantime.

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Protesters against the cost-cutting targeted Tesla dealerships while arsonists even torched a few of the electric vehicles, and the firm's profits slumped.

"People were burning Teslas. Why would you do that? That’s really uncool," Musk told the Post.

Musk has also been focusing on Space X after a series of fiery setbacks to his dreams of colonizing Mars -- the latest of which came on Tuesday when its prototype Starship exploded over the Indian Ocean.

The tycoon last week also said he would pull back from spending his fortune on politics, having spent around a quarter of a billion dollars to support Trump. -- Danny Kemp

© Agence France-Presse