US President Donald Trump has attacked the World Health Organization (WHO) for being too "China-centric" in its tackling of the coronavirus pandemic.
"The WHO really blew it," the president said, adding that he was considering withdrawing funding to the UN agency.
The US is one of the agency's largest voluntary contributors.
The WHO later rejected Mr Trump's comments, saying that working closely with China was "absolutely essential" in understanding the disease.
Covid-19 first emerged last December in the Chinese city of Wuhan, which has just ended an 11-week lockdown.
On Tuesday, Mr Trump accused the WHO of being biased towards China in how it issued its guidance during the outbreak.
The president has himself faced criticism for his administration's slow response to the pandemic, including problems with early testing.
The US decided against using a coronavirus test approved by the WHO in January, in favour of a test being developed by the Centers for Disease Control and Prevention (CDC).
In February, the CDC despatched testing kits across the US - but some of them did not work properly, and led to inconclusive results.
Although the US is now carrying hundreds of thousands of tests a day, critics say that the early testing failures were crucial in allowing the virus to spread more widely. President Trump also often downplayed the seriousness of the outbreak during this period.
What did Trump say?
Speaking during the daily Coronavirus Task Force briefing at the White House on Tuesday, Mr Trump said his administration would take "a good look" at its contributions to the WHO, while questioning some of the UN agency's advice.
"They called it wrong," he said, adding: "They really, they missed the call. Fortunately, I rejected their advice on keeping our borders open to China early on. Why did they give us such a faulty recommendation?"
On US financial contributions to the WHO, he said: "We're going to put a hold on money spent... we're going to put a very powerful hold on it and we're going to see."
His remarks came as the US recorded a daily death toll from Covid-19 of more than 1,800. The country has nearly 400,000 known infections, according to figures compiled by Johns Hopkins University.
How has the WHO responded?
A UN spokesman, Stephane Dujarric, rejected Mr Trump's criticism, saying that the WHO's Director General Dr Tedros Adhanom Ghebreyesus had "done tremendous work" in providing guidance as Covid-19 travelled around the world.
"For the Secretary General [Antonio Guterres], it is clear that the WHO... is showing the strength of the international health system," Mr Dujarric said, adding that the agency was supporting numerous countries with equipment and training.
Dr Bruce Aylward, head of the joint WHO-Chinese mission on Covid-19, responded to Mr Trump's comments by saying it was "absolutely essential that we work closely with China to understand this disease".
The WHO's regional director for Europe, Dr Hans Kluge, said that now was "not the time to cut back funding" as the pandemic was at its acute phase.
How is the WHO funded?
The WHO relies on funding from both government and private sources. Its funding is also split into mandatory and voluntary contributions, with the last one becoming increasingly important over the years.
In the last financial year, more than 80% of WHO funds came from voluntary contributions made by governments, private organisations like charities, and other UN agencies as well as multilateral bodies like the EU.
The US government is the largest of these voluntary contributors, accounting for just under 15% of WHO funding in 2019. But the next biggest was the Bill and Melinda Gates Foundation, making up nearly 10% of funding.
Other countries which made significant voluntary contributions in 2019 include the UK (7.8%) and Germany (5.7%).
It is worth adding that the US also owes the WHO most in terms of mandatory contributions. Figures for March 2020 show that the US still had more than $99m (£80m) in outstanding payments, much more than anyone else.
What did Trump say about ventilators?
Mr Trump said the US would have an additional 110,000 ventilators coming "over a short period of time". However, he did not provide an exact timeline and went on to say that the majority - 60,000 devices - would not be received until 29 June.
He said that this would create a surplus, and that extra ventilators could be distributed to help those "desperate" countries fighting the virus, including the UK.
The US "won't need anywhere near" the additional devices that it will have at its disposal, he said.
New York Governor Andrew Cuomo recently signed an order allowing the state to redeploy ventilators from "across the system". "There are hospitals that have ventilators, that have PPE equipment... that we are going to need," he said.
Mr Trump said the UK had already requested 200 devices, adding: "We're going to work it out, we've got to work it out - they've been great partners, the United Kingdom."
Ventilators are vital in the treatment of some patients suffering from coronavirus, which can cause severe respiratory issues while the infection attacks the lungs. The devices can help keep patients breathing.