US President Donald Trump has said he has instructed his administration to halt funding to the World Health Organization (WHO).
He said the WHO had “failed in its basic duty” in its response to the coronavirus outbreak.
He accused the UN body of mismanaging and covering up the spread of the virus after it emerged in China, and said it must be held accountable.
Mr Trump has previously accused the WHO of being biased towards China.
The US president has himself come under criticism at home over his handling of the outbreak.
“I am directing my administration to halt funding while a review is conducted to assess the World Health Organization’s role in severely mismanaging and covering up the spread of the coronavirus,” Mr Trump told a news conference at the White House.
“The WHO failed in its basic duty and it must be held accountable,” he added.
America is the WHO’s biggest single funder, providing $400m (£316m) last year – just under 15% of its total budget.
“With the outbreak of the Covid-19 pandemic, we have deep concerns whether America’s generosity has been put to the best use possible,” the president said.
The US is the worst-affected country in the coronavirus pandemic with 592,743 cases and 25,239 deaths.
Speaking in the Rose Garden at the White House, President Trump also said that plans to reopen the country were “close to being finalised”.
“I will be speaking to all 50 governors very shortly and I will be authorising each individual governor of each individual state to implement a plan,” he said.
Mr Trump caused a furore on Monday when he said that he, and not state governors, had the authority to lift lockdowns and restart the economy.
Earlier on Tuesday, New York Governor Andrew Cuomo accused President Trump of “spoiling for a fight”.
New York state has the most cases, with almost 190,000 cases and over 10,000 deaths. However, there are signs of improvement with the number of people there needing hospital treatment falling for the first time.