US President Donald Trump has sent a letter to the head of the World Health Organization (WHO) threatening to pull US funding permanently over Covid-19.
The letter outlines a 30-day deadline for the body to commit to "substantive improvements" or risk losing millions and US membership altogether.
Addressed to WHO chief Tedros Adhanom Ghebreyesus, it criticises stages of the body's response since December.
Earlier on Monday, Mr Trump called the UN's health body a "puppet of China".
The president, who faces re-election this year and has himself been criticised for his handling of the pandemic, has blamed China for trying to cover up the outbreak and has accused the WHO of failing to hold Beijing to account.
Chinese foreign ministry spokesman Zhao Lijian said Mr Trump was trying to mislead the public, smear China and "shift the blame for [the US's] own incompetent response".
The US has more than 1.5 million of the world's 4.8 million confirmed cases of coronavirus so far, with more than 90,000 deaths.
Mr Trump's ultimatum also comes at a time of pressure for the WHO.
On Monday Dr Tedros backed a review of the agency's handling of the pandemic. He said an independent evaluation would take place "at the earliest appropriate moment".
Mr Trump published the letter on Twitter on Monday night, following a day of heavy US criticism of the health agency.
Health Secretary Alex Azar spoke at the WHO's World Health Assembly and accused the organisation of letting Covid-19 spin "out of control" at the cost of "many lives".