The World Health Organisation says an independent review of the global coronavirus response will begin as soon as possible, and it received backing and a hefty pledge of funds from China.
But the US administration of President Donald Trump 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.
Without mentioning China by name, US Health Secretary Alex Azar made clear Washington considered the WHO jointly responsible for the pandemic.
"We must be frank about one of the primary reasons this outbreak spun out of control," he said on Monday.
"There was a failure by this organisation to obtain the information that the world needed, and that failure cost many lives."
WHO director-general Tedros Adhanom Ghebreyesus defended the organisation's response.
"WHO sounded the alarm early, and we sounded it often," he said.
When the WHO declared a global emergency on 30 January there were fewer than 100 cases outside China, and no deaths, Tedros added.
Tedros was addressing a virtual meeting of the WHO's decision-making body, the World Health Assembly.
Chinese President Xi Jinping said China had acted with "openness and transparency and responsibility".
Tedros, who has always promised a coronavirus review, told the forum it would come "at the earliest appropriate moment" and make recommendations for the future.
He received robust backing from the WHO's independent oversight panel.
"Every country and every organisation must examine its response and learn from its experience," Tedros said, adding that the review must cover "all actors in good faith".
In its first report on the handling of the pandemic, the seven-member oversight committee said the WHO had "demonstrated leadership and made important progress in its Covid-19 response".
The panel endorsed a review, but said conducting it now could hamper the WHO's response to the pandemic.
It also said "an imperfect and evolving understanding" was not unusual when a new disease emerged.
In an apparent rejoinder to Trump, the panel said a "rising politicisation of pandemic response" was hindering the effort to defeat the virus.
A resolution drafted by the EU calling for an independent evaluation of the WHO's performance appeared to have won consensus backing among the WHO's 194 states. It was expected to be debated and adopted on Tuesday.
China has previously opposed calls for a review of the origin and spread of the coronavirus, but Xi signalled that Beijing would accept an impartial evaluation of the global response, once the pandemic is brought under control.
"This work needs a scientific and professional attitude, and needs to be led by the WHO. And the principles of objectivity and fairness need to be upheld," he told the meeting via video.
"All along we have acted with openness and transparency and responsibility."
He pledged $US2 billion over the next two years to help deal with Covid-19, especially in developing countries.
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