President Donald Trump attacked the United Nations health body as a Chinese "puppet" on Monday and confirmed he is considering slashing or cancelling US support.
"They're a puppet of China, they're China-centric to put it nicer," he said at the White House.
Trump said the United States pays around $450 million annually to the World Health Organization, the largest contribution of any country.
Plans are being crafted to slash this because "we're not treated right."
"They gave us a lot of bad advice," he said of the WHO.
'Sad job'
Trump spoke as the WHO held its first annual assembly since the pandemic swept the world after originating in China, causing massive economic disruption and killing over 319,000 people, close to a third of them in the United States.
He would issue a statement about WHO in the near future and said it had "done a very sad job" in its handling of the coronavirus.
Trump told a White House event he would make a decision about US' WHO funding soon, and that he had considered reducing it to $40 million, but some felt that was too much.
Asked why he had not addressed a virtual ministerial meeting of the WHO earlier in the day, he replied: "I chose not to make a statement today. I'll be giving them a statement, sometime in the near future, but I think they've done a very sad job in the last period of time."
WHO's 'failure cost many lives'
Earlier, WHO said an independent review of the global coronavirus response would begin as soon as possible and it received backing and a hefty pledge of funds from China, in the spotlight as the origin of the pandemic.
But the WHO's chief critic, the US administration, decried an "apparent attempt to conceal this outbreak by at least one member state".
Trump has already suspended US funding for the WHO after accusing it of being too China-centric, and at the same time led international criticism of Beijing's perceived lack of transparency in the early stages of the crisis.
Health Secretary Alex Azar did not mention China by name but made clear Washington considered the WHO jointly responsible.
"We must be frank about one of the primary reasons this outbreak spun out of control," he said.
"There was a failure by this organisation to obtain the information that the world needed, and that failure cost many lives."
China pledges $2 billion
Speaking after Azar, Chinese Health Minister Ma Xiaowei said Beijing had been timely and open in announcing the outbreak and sharing the virus's full gene sequence, and urged countries to "oppose rumours, stigmatisation and discrimination".
Chinese President Xi Jinping pledged $2 billion over the next two years to help deal with Covid-19, especially in developing countries.
The amount almost matches the WHO's entire annual programme budget for last year, and more than compensates for Trump's freeze of US payments worth about $400 million a year.
But White House National Security Council spokesman John Ullyot called it "a token to distract from calls from a growing number of nations demanding accountability for the Chinese government’s failure to warn the world of what was coming".