A US Senate committee chairman has warned ex-White House chief medical adviser Anthony Fauci could be held in contempt of Congress after he refused to answer questions at a combative hearing into his handling of the Covid pandemic.

The former top infectious disease expert invoked his constitutional right against self-incrimination during testimony more than 100 times.

Senator Rand Paul of Kentucky said afterwards: "I think there is a very real chance that he could be prosecuted for that."

Paul has long accused Fauci of trying to cover up the origin of the coronavirus, and of funding research at a lab in Wuhan in China, where some theories say the pandemic began. Fauci has denied wrongdoing.

It remains unclear whether he could face any charges.

The former head of the National Institute of Allergies and Infectious Diseases was grilled on Wednesday by the Senate Committee on Homeland Security and Governmental Affairs.

He told the panel he was invoking the Fifth Amendment to the US Constitution under the advice of his attorneys.

Invoking the Fifth in itself is not a crime, and is routinely used by defendants in criminal investigations at every level of the US judicial system.

President Donald Trump invoked the Fifth repeatedly in a deposition for a civil case against the Trump Organization in New York back in 2022, before he returned to the White House.

Paul, a Kentucky senator, said the committee would vote next week on holding Fauci in criminal contempt of Congress.

If approved, the resolution would go to the Senate floor, according to the BBC's US partner CBS. But it would need 60 votes to pass - a longshot since that would require Democrats to side with Republicans.

If it were passed through the Senate, it would be referred to the top prosecutor for the District of Columbia for possible prosecution.

Before leaving office, President Joe Biden issued a pre-emptive pardon to Fauci covering his actions between 2014-25.

But Fauci could still face charges for anything after that date, including in his actions towards the Senate committee.

Paul, who is chairman of the panel, acknowledged the issue of Fauci's pardon, and whether it imparted him immunity, was "another legal question that the courts may have to decide upon".

Presidential pardons only cover federal offences, not state-level cases. Florida's top prosecutor said on Wednesday he would investigate Fauci.

But Attorney General James Uthmeier provided no details about what crimes he believed Fauci might allegedly have committed.

Paul has repeatedly argued that Covid probably leaked from China's Wuhan Institute of Virology - a theory that the CIA backed last year.

In the hearing, the senator suggested that while Fauci had said publicly that Covid originated naturally, his diaries indicated he privately believed the virus originated in a medical lab.

Republicans asked Fauci about shifting health guidance, which changed during the pandemic as health officials learned more about the disease. Fauci has previously defended his policy positions.

But several Democrats came to Fauci's defence, including Senator Maggie Hassan, who said the hearing was "designed to entrap" him.

President Trump, meanwhile, took to social media to call Fauci "crazy".

"I said from the beginning that the Virus came from the Wuhan Laboratory in China. Fauci strongly disagreed, always trying to protect China," he said.

The World Health Organization said last year the natural-origin theory - the virus spilling over from animals to people - was the "best supported" idea from available evidence, but that until more information emerges, the matter is "inconclusive".

Fauci has faced death threats during and after the coronavirus pandemic. Trump last year removed his security protection.

The former top health official was one of the most trusted members of the US government during its response to the pandemic as scientists were trying to learn about the virus as quickly as possible.

He was not always at loggerheads with Trump. In 2021, Trump awarded Fauci a presidential commendation for his work on the US Covid vaccine project, known as Operation Warp Speed. (BBC)

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