President Donald Trump on Friday said USAID should "close," in an escalation of his already unprecedented campaign to dismantle the massive government aid agency.

"THE CORRUPTION IS AT LEVELS RARELY SEEN BEFORE. CLOSE IT DOWN!" Trump wrote in a trademark all-caps statement on his Truth Social app.

Trump, who began his second term last month, has launched a crusade led by his top donor and world's richest man Elon Musk to downsize or dismantle swaths of the US government.

The most concentrated fire has been on the United States Agency for International Development, the primary organization for distributing US humanitarian aid around the world.

The Trump administration has ordered thousands of foreign-based staff to return to the United States and frozen foreign aid.

On Thursday a report in The New York Times said the current USAID headcount of 10,000 employees would be reduced to around 300.

Labor unions are challenging the legality of the onslaught which includes offers of buyouts by Musk to federal workers across the entire government.

Democrats in Congress say it would be unconstitutional for Trump to shut down government agencies without the greenlight from the legislature.

Trump has also announced he wants to close the Department of Education.

The United States' current budget allocates about $58 billion for international assistance.

However while Washington is the biggest aid donor in the world, the money has amounted to no more than 0.7 to 1.4 percent of total government spending in the last quarter century, according to the Pew Research Center.

USAID runs 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 United States in its struggle for influence with rivals including China, where Musk has extensive business interests.

Hard-right Republicans and libertarians have long questioned the need for USAID and criticized what they say is wasteful spending abroad.

Those criticisms have been supercharged since Trump's return with the administration demonizing USAID employees and claiming — without evidence — that the aid agency is rife with fraud.

"USAID IS DRIVING THE RADICAL LEFT CRAZY," Trump wrote in his post. "SO MUCH OF IT FRAUDULENTLY, IS TOTALLY UNEXPLAINABLE. THE CORRUPTION IS AT LEVELS RARELY SEEN BEFORE."