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(NEXSTAR) – A recurring clash between the government’s top infectious disease doctor and a U.S. senator has erupted again on Capitol Hill, with each accusing the other of lying.

Dr. Anthony Fauci angrily confronted Republican Sen. Rand Paul of Kentucky in testimony before a Senate committee on Tuesday. Fauci rejected Paul’s insinuation that the U.S. helped fund research at a Chinese lab that could have sparked the COVID-19 outbreak.

Fauci spoke to the Senate Health, Education, Labor, and Pensions Committee, saying a study the senator mentioned referenced a different sort of virus entirely from the one responsible for the coronavirus outbreak.

“Senator Paul, you do not know what you’re talking about, quite frankly,” Fauci said. “And I want to say that officially. You do not know what you’re talking about.”

He added, “If anybody is lying here, senator, it is you.”

It was the latest in a series of clashes between Paul and Fauci about the origins of the virus that caused the global pandemic.

Paul, an ophthalmologist prior to entering politics, has used such hearings to grill Fauci about his prior statements on the pandemic.

Last fall, an exasperated Fauci told the Kentucky senator he was ‘not listening’ as the two discussed the effectiveness of New York’s response to the pandemic.