Musk, who is also CEO of Tesla and SpaceX, discussed the Department of Government Efficiency (DOGE) in a social media talk on Monday on X, which he also owns.
Trump has assigned Musk to lead a federal cost-cutting panel.
The conversation, which included former Republican presidential candidate Vivek Ramaswamy and Republican Senators Joni Ernst and Mike Lee, began with Musk saying they were working to shut down the United States Agency for International Development (USAID).
"It's beyond repair," Musk said, adding that Trump agrees it should be shut down.
Meanwhile, most USAID staffers were told not to report to the agency's headquarters in Washington DC on Monday and to work remotely, according to a copy of an email to personnel reviewed by Reuters.
"Further guidance will be forthcoming," the note said.
On Sunday, Reuters reported Trump's administration removed two top security officials at USAID during the weekend after they tried to stop DOGE representatives from gaining access to restricted parts of the building, three sources said.
Trump later on Sunday told reporters that USAID has "been run by a bunch of radical lunatics," adding: "We're getting them out, and then we'll make a decision".
The United States is the world's largest single donor.
In fiscal year 2023, the US disbursed $US72 billion ($A116 billion) of assistance worldwide on everything from women's health in conflict zones to access to clean water, HIV/AIDS treatments, energy security and anti-corruption work.
It provided 42 per cent of all humanitarian aid tracked by the United Nations in 2024.
The website of USAID appeared to still be offline on Saturday and some users could not access it on Sunday.
USAID has a staff of more than 10,000 people.
Trump has ordered a global freeze on most US foreign aid as part of his "America First" policy which is already sending shockwaves around the world.
Speaking more broadly about cutting US expenses and fraud, Musk estimated the Trump administration can cut $US1 trillion from the US deficit next year.
He asserted, for example, that "professional foreign fraud rings" are stealing vast sums by masquerading as or creating fake digital US citizens.
Musk did not offer any evidence to support his fraud claim or explain how he reached the figure of $US1 trillion.
Asked on Sunday if Musk was doing a good job, Trump said: "He's a big cost-cutter. Sometimes we won't agree with it and we'll not go where he wants to go. But I think he's doing a great job."
Musk's team has been given access to or has taken control of numerous government systems.
Musk has moved swiftly to install allies at the agency known as the Office of Personnel Management.
A team including current and former employees of Musk assumed command of OPM on January 20, the day Trump took office, the sources added.
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