In this file photo taken on March 22, 2022, Tesla CEO Elon Musk is pictured as he attends the start of the production at Tesla's "Gigafactory" in Gruenheide, southeast of Berlin. - Twitter's shares soared after Tesla CEO Elon Musk disclosed on April 4, 2022, a large stake in the social media company, which he has criticized for its approach to speech rights. Patrick Pleul, POOL / AFP

WASHINGTON — Elon Musk, the billionaire advisor to Donald Trump, said Saturday that all US federal employees must justify their work or lose their jobs, hours after the president pushed him to be "more aggressive" in slashing government spending.

Musk — the world's richest person and Trump's biggest donor — has led the effort to fire swaths of the government workforce.

"All federal employees will shortly receive an email requesting to understand what they got done last week. Failure to respond will be taken as a resignation," Musk wrote.

According to a copy of the email provided to AFP, federal workers were asked to submit "approx. 5 bullets of what you accomplished last week."

The email came from the US Office of Personnel Management, with the subject line "What did you do last week?". The deadline to reply was 11:59 pm Monday, though the message did not say failure to do so would lead to termination.

Musk defends DOGE cuts during CPAC appearance

Earlier Saturday, Trump said on his Truth Social platform that Musk was "doing a great job, but I would like to see him get more aggressive."

"Remember, we have a country to save," the Republican leader added.

Trump has put the tech entrepreneur in charge of the new Department of Government Efficiency (DOGE), tasking him with slashing public spending and tackling waste and alleged corruption.

In the latest cuts announced Friday, the US Defense Department is to reduce its civilian workforce by at least five percent starting next week.

Trump's administration has already begun firing many other federal workers who are on probationary status.

DOGE is a free-ranging entity run by Musk, though its cost-cutting spree has been met with pushback on several fronts and mixed court rulings.

A judge on Thursday denied a union bid to temporarily halt the firing of thousands of people.

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Musk said this week he would work with Trump for as long as he "can be helpful," as the pair dismissed concerns over conflicts of interest due to the tech tycoon's government contracts.

"Elon is doing a great job," Trump told a meeting of conservative activists on Saturday, running through a list of what he said were "some of the flagrant scams" that had been uncovered.

"We love Elon, don't we? He's a character," Trump added. "People said, what official position does he have? I said, 'Patriot'."

Musk said this week DOGE was publicizing its actions on its website and that the transparency would hold him accountable.

© Agence France-Presse