Former U.S. chief medical adviser Anthony Fauci has refused to answer questions from a Republican-led Senate committee investigating the origins of the COVID-19 pandemic.

On Wednesday, before the U.S. Senate Homeland Security and Governmental Affairs Committee, Republican lawmakers accused the health expert of concealing information about the virus’s origin and helping finance a research lab in Wuhan, China.

Mr Fauci declined to respond to questions on allegations surrounding the pandemic that might be used against him, invoking his constitutional right against self-incrimination during testimony.

He said, “Because of the respect I have for the legislative branch and my decades-long record of cooperating with Congress, under the advice of my attorneys, I will invoke my right under the Fifth Amendment of the Constitution to refrain from answering your questions.

“Although it pains me to do so because of the respect I have for the legislative branch and my decades-long record of cooperating with Congress, under the advice of my attorneys, I will invoke my right under the Fifth Amendment of the Constitution to refrain from answering your questions.”

President Donald Trump also weighed in on the case, calling Mr Fauci “crazy” on social media.  

“I said from the beginning that the virus came from the Wuhan Laboratory in China. Fauci strongly disagreed, always trying to protect China,” Mr Trump wrote.

The World Health Organisation said last year that the strongest evidence showed the virus spread naturally from animals to humans. But the exact origin of COVID-19 has not been confirmed.

Mr Fauci received death threats during and since the coronavirus pandemic. Last year, Mr Trump withdrew the government-funded security protection that had been provided to Mr Fauci.