WASHINGTON, United States (AFP) — The US government’s giant humanitarian agency closed its headquarters to staff Monday amid moves by Elon Musk, the world’s richest person and President Donald Trump’s controversial aide, to seize control in actions decried by critics as “plain illegal.”

Workers at the US Agency for International Development (USAID) were told to stay out of its Washington office after its website went dark over the weekend, with Secretary of State Marco Rubio announcing Monday it would come under his control.

Rubio said in a statement the agency had “long strayed from its original mission of responsibly advancing American interests abroad” and that he was launching a review of its activities ahead of a “potential reorganization.”

But there was widespread confusion, as some 600 staffers found themselves locked out of their computer systems, ABC News reported.

Democrats were denied entry to the public lobby of the agency’s headquarters by police blocking the doors as they joined around 50 demonstrators brandishing banners demanding: “Save USAID, save lives.”

They blasted Trump for handing administration policy to an unelected tycoon who has undergone no background checks or confirmation process and has glaring conflicts of interest as one the largest government contractors.

“This is a brazen attempt by a billionaire who nobody voted for, to illegally and unconstitutionally steal from taxpayers so he can give himself a tax break,” said Massachusetts Congressman Jim McGovern.

Virginia Congressman Gerry Connolly angrily insisted that Musk had no legal right to shutter an organization created by an act of Congress.

“It is a matter of statute. It’s a matter for Congress to deal with, not an unelected billionaire oligarch named Elon Musk,” he said. “And Elon, if you want to run USAID, get nominated by Trump and go to the Senate. Good luck in getting confirmed.”

The aid arm of US foreign policy, USAID funds health and emergency programs in around 120 countries, including the world’s poorest regions.

It is seen as a vital source of soft power for the US in its struggle for influence with rivals including China, where Musk has extensive business interests.

The SpaceX and Tesla CEO called USAID “a viper’s nest of radical-left marxists who hate America” and added that he had personally cleared the unprecedented move with the president.