Washington DC - The US on Tuesday released a new policy curtailing funding for a form of biological research President Donald Trump's administration says caused the Covid-19 pandemic through a lab leak in China.

Under the new policy, the US will halt funding in certain countries for so-called "gain-of-function" experiments, which are aimed at enhancing the properties of pathogens with the intention of better predicting emerging infectious diseases and supporting the development of treatments, including vaccines.

The policy jointly announced Tuesday by the US State Department and Health and Human Services fulfills Trump's May 2025 executive order regarding such research.

"The new policy prohibits federal support for dangerous gain-of-function research conducted in the United States and abroad, establishes rigorous independent review for certain high-risk life sciences research, and restricts federal funding for research conducted in countries or institutions that lack appropriate biosafety, biosecurity, and oversight standards," detailed HHS in a statement.

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The State Department called the new policy "an America First approach to scientific research."

"The new policy preserves the benefits of life-sciences research while defining the areas of greatest risk, including prevention of accidental or intentional lab leaks, and penalties for irresponsible practices," wrote Jay Bhattacharya, director of the National Institutes of Health, in a Wall Street Journal op-ed published Tuesday.

Trump has long championed the theory that SARS-CoV-2 leaked from the Wuhan Institute of Virology as a result of gain-of-function research – an alternative to the theory that the virus spilled over naturally from wild animals to humans at a seafood market in the same city.

Washington's former top infectious disease official, Anthony Fauci, has insisted that the US did not fund such research in China.

The new US policy comes as Fauci's private diary has gone public, released by Republican Senator Rand Paul. The leak includes entries that highlight disagreement over the origins of Covid-19 as the pandemic was quickly unfolding.

Fauci is scheduled to testify before a Senate committee on Wednesday.