Donald Trump has been condemned for his "dangerous" decision to halt US payments to the World Health Organisation in the midst of the coronavirus pandemic.
The US president says the WHO "failed in its basic duty" to stop the virus spreading when it was first reported in China, and "must be held accountable".
The US gave 900 million dollars (£720 million) to the WHO in the year 2018-2019 - a fifth of its total budget for that year.
Mr Trump said he would be "putting a hold on all funds going to World Health" during an "evaluation period" he says will last between 60 and 90 days.
Fellow billionaire Bill Gates has hit out at Mr Trump's decision, labelling it "dangerous as it sounds".
He said no organisation could replace its work, adding the "world needs WHO now more than ever".
European Union foreign policy chief Josep Borrell said the 27-nation EU “deeply” regrets the suspension of funds and added that the WHO is “needed more than ever” to combat the pandemic.
He called for measures to promote unity instead of division, and said: “Only by joining forces can we overcome this crisis that knows no borders.”
A Chinese foreign ministry spokesman said the country is “seriously concerned” about the US decision, telling reporters: “As the most authoritative and professional international institution in the field of global public health security, the WHO plays an irreplaceable role in responding to the global public health crisis.”
Spokesman Zhao Lijian said the US move will “weaken the WHO’s capabilities and undermine international co-operation in fighting the epidemic”.
UN secretary-general Antonio Guterres responded to Mr Trump’s announcement by saying now is not the time to end support, calling the WHO “absolutely critical” to the global effort to combat Covid-19.
Mr Guterres said the appropriate time for a review is “once we have finally turned the page on this pandemic”.
The US President claimed the outbreak could have been contained at its source and spared lives had the UN health agency done a better job of investigating reports coming out of China.
He continued that the world depends on the WHO to work with countries to make sure accurate information about health threats are shared in a timely manner.
The US contributed nearly 900 million dollars (£720 million) to the WHO’s budget for 2018-19, according to the agency’s website. That represents a fifth of its total budget for those years.
Washington gave nearly three-quarters of the funds in “specified voluntary contributions” and the rest in “assessed” funding as part of the commitment to UN institutions.
Last week, Mr Trump blasted the WHO for being “China-centric” and alleging that it had “criticised” his ban on travel from China as the Covid-19 outbreak was spreading from the city of Wuhan.
In a White House briefing, Mr Trump said: "The WHO failed in its basic duty and must be held accountable.”
He added the US will continue to engage with the global health organisation in pursuit of what he called meaningful reforms.
The US has seen 26,000 deaths of people who have tested positive for coronavirus, the highest number of any country in the world.
As cases in the US passed more than 610,000, Mr Trump said a "strong" plan to reopen the US was being "finalised".
Coronavirus: Everything you need to know: