Payments would be held for up to 90 days, during which time the administration would investigate the agency’s response, and a resumption in payments would be contingent on the outcome of the inquiry, Trump said.

With its payments accounting for about 15 per cent of the organisation’s US$6.2 billion budget over the past two years, the US is the WHO’s biggest contributor. Washington’s outlays of foreign aid, including to the WHO, must be approved by Congress as part of the annual federal budget.

The Impoundment Control Act of 1974 stipulates that a president can withhold such funding for up to 45 days, only after “a special message to Congress identifying the amount of the proposed rescission; the reasons for it; and the budgetary, economic and programmatic effects of the rescission”.

Withholding beyond that time frame would require an act of Congress.

The American Medical Association (AMA) also called Trump’s decision “dangerous”.

“During the worst public health crisis in a century, halting funding to the World Health Organisation is a dangerous step in the wrong direction that will not make defeating Covid-19 easier. Fighting a global pandemic requires international cooperation and reliance on science and data,” AMA president Patrice Harris said.

“Cutting funding to the WHO – rather than focusing on solutions – is a dangerous move at a precarious moment for the world. The AMA is deeply concerned by this decision and its wide-ranging ramifications, and we strongly urge the president to reconsider.”

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Trump may have a legal basis for cutting at least some of the funding.

“There are doubtlessly reasonable grounds for criticism of the WHO, although the administration’s focus on it is intended to distract from its own handling of the crisis, to continue advancing efforts begun in 2017 to reduce American funding for international health efforts, as well as to further its particularly xenophobic and jingoistic framing of the crisis,” said David Alexander Bateman, an assistant professor at Cornell University’s department of government.

“The administration, however, might be on sound legal footing for cutting off some sources of WHO funding, although much will hinge on the specific language of the relevant authorisations and appropriations that have passed Congress.”

US funding for the WHO was divided into assessed dues, which were currently set at 22 per cent of all member states’ dues, and voluntary contributions, which varied from year to year, Bateman said.

Voluntary contributions cannot be withheld, but the Trump administration aims to divert this portion and the non-disbursed portion of the assessed dues to other foreign aid agencies.

Other prominent voices have also joined the call for Trump to back away from the punitive measures.

“Halting funding for the World Health Organisation during a world health crisis is as dangerous as it sounds,” Microsoft co-founder Bill Gates said on Twitter on Wednesday.

“Their work is slowing the spread of Covid-19 and if that work is stopped no other organisation can replace them.”

After the US, the Bill & Melinda Gates Foundation is the second largest donor to the WHO, accounting for almost 10 per cent of its funding with a US$531 million contribution. The foundation has also pledged US$100 million to help contain the coronavirus outbreak.

The US Chamber of Commerce, which includes among its 3 million members multinational manufacturing giants such as Ford and IBM, called the WHO “critical”.

“The chamber supports a reformed but functional World Health Organisation, and US leadership and involvement are essential to ensuring its transparency and accountability going forward,” the industry association said.

“However, cutting the WHO’s funding during the Covid-19 pandemic is not in US interests given the organisation’s critical role assisting other countries – particularly in the developing world – in their response.”