Trump, who has reacted angrily to criticism of his administration's response to the worst epidemic in a century, has become increasingly hostile towards the WHO.
The Geneva-based organisation had promoted China's "disinformation" about the virus that likely led to a wider outbreak than otherwise would have occurred, Trump said.
"The WHO failed in this basic duty and must be held accountable," Trump told a White House news conference on Tuesday.
Nearly 2 million people globally have been infected and more than 124,000 have died since the disease emerged in China late last year, according to a Reuters tally.
U.N. Secretary-General Antonio Guterres said it was not the time to reduce resources for the WHO.
"Now is the time for unity and for the international community to work together in solidarity to stop this virus and its shattering consequences," he said in a statement.
The United States is the biggest overall donor to the WHO, contributing more than $400 million in 2019, roughly 15% of its budget.
Australian Prime Minister Scott Morrison said he sympathised with Trump's criticisms of the WHO, especially its "unfathomable" support of re-opening China's "wet markets", where freshly slaughtered, and live, animals are sold.
The coronavirus is believed to have emerged from such a market in the city of Wuhan late last year.
"But that said, the WHO also as an organisation does a lot of important work including here in our region in the Pacific and we work closely with them," Morrison told an Australian radio station.
"We are not going to throw the baby out of with the bathwater here, but they are also not immune from criticism."
More than 2,200 people died in the United States on Tuesday, a record toll according to a Reuters tally, even as it debated how to reopen its economy.
New York City, the U.S. city hardest hit by the outbreak, revised its death toll sharply up to more than 10,000, to include victims presumed to have died of the lung disease but never tested.
U.S. health advocacy group Protect Our Care said Trump's WHO funding withdrawal was "a transparent attempt … to distract from his history downplaying the severity of the coronavirus crisis and his administration’s failure to prepare our nation".
"To be sure, the World Health Organization is not without fault but it is beyond irresponsible to cut its funding at the height of a global pandemic," said Leslie Dach, the group's chair.
'NOT SEEING PEAK YET'
The WHO said the number of new cases were tailing off in some places, such as Italy and Spain, but outbreaks were growing in Britain and Turkey.
"The overall world outbreak – 90% of cases are coming from Europe and the United States of America. So we are certainly not seeing the peak yet," WHO spokeswoman Margaret Harris told a briefing in Geneva.
Dozens of cases have been recorded among oil and gas workers in Brazil, the industry regulator told Reuters, exposing an outbreak far worse than thought.
India extended a lockdown on its 1.3 billion people until May 3 as its tally of cases exceeded 10,000. Prime Minister Narendra Modi said economic sacrifices were needed to save lives.
New cases in China dropped to 46, compared with 89 the previous day, officials reported on Wednesday, with one more death. Most cases were people returning from Russia.
Asian share markets edged higher as China moved again to cushion its economy, cutting a key medium-term interest rate to record lows and paving the way for a similar reduction in benchmark loan rates. [MKTS/GLOB]
The global economy is expected to shrink by 3% this year, the International Monetary Fund said, marking the steepest downturn since the Great Depression.
Major international creditors will relieve the world's poorest countries of debt payments this year, France announced.
Japan's Prime Minister Shinzo Abe came under pressure to hand out more cash to help cushion the blow on top of a near $1 trillion package announced last week.
Trump, who has declared he will decide when to lift U.S. lockdowns, suggested some Democratic state governors were "mutineers" after New York Governor Andrew Cuomo said he would refuse any order that risked reigniting the outbreak.
Trump's top infectious disease adviser, Dr Anthony Fauci, said the president's May 1 target for restarting the economy was "overly optimistic".
Airlines have been hit hard as borders have closed and people stay at home.
China's airlines reported a total loss of $4.8 billion in the first quarter, its regulator said.
The U.S. Treasury Department said major passenger airlines had agreed in principle to a $25 billion rescue package, ensuring their workers have jobs until October while the industry battles its biggest-ever crisis.
In New Zealand, where a strict lockdown has limited the number of cases and deaths, Prime Minister Jacinda Ardern announced she, her ministers and public service chief executives would take a 20% pay cut for six months.