EXCLUSIVE: House Republicans are demanding Dr. Anthony Fauci explain his emails on the coronavirus pandemic they argue undercut his public statements that the U.S. did not fund gain-of-function research at a Chinese lab. 

Reps. Chip Roy, R-Texas, and Bill Posey, R-Fla., led a letter – first obtained by Fox News – to the nation's top infectious disease expert in which they accuse him of appearing to "mislead the American people on the origins of COVID-19 and gain-of-function research."

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"He testified before the Senate that risky gain-of-function research was not occurring in Wuhan, yet in his now-public emails, sends an urgent message to his deputy on gain-of-function," Roy told Fox News Wednesday. "His emails also implicate him in having influence over a paper that called the lab leak theory implausible. 

(Photo By Tom Williams/CQ-Roll Call, Inc via Getty Images)

Rep. Chip Roy, R-Texas, says Dr. Anthony Fauci mislead the American people about gain of function research in China. (Tom Williams/CQ-Roll Call, Inc via Getty Images)

"The American people deserve answers about what Fauci knew and when he knew it; we must investigate this and see wherever the truth leads us."

The group of 13 lawmakers fired off a series of specific questions to Fauci about his emails, which were recently published by news outlets thanks to Freedom of Information Act (FOIA) requests. They suggest that Fauci's email communications contradict his public statements that the National Institutes of Health (NIH) did not fund so-called "gain-of-function" research at a Wuhan virology lab.

As the lab-leak theory has gained credibility after being widely dismissed in the press last year, there's more attention being paid to monies given to the Wuhan Institute of Virology, known for its bat coronavirus research and so-called "gain of function" methods, which involves manipulating viruses to make them more infectious for research.

Sen. Rand Paul, R-Ky., and Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. (Bill Clark/CQ-Roll Call, Inc. | Stefani Reynolds/The New York Times/Bloomberg via Getty Images)

Fauci, the director of the National Institute of Allergy and Infectious Diseases, has repeatedly denied any NIH money went to such research in Wuhan, but his organization has given millions of dollars in grant money to the EcoHealth Alliance, a research nonprofit that funneled at least $600,000 to Wuhan coronavirus research.

The letter builds off of tense exchanges between Sen. Rand Paul, R-Ky., and Fauci where Paul accused President Biden's chief medical adviser of being dishonest about what NIH funded. 

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Fauci has testified before Congress stating multiple times that NIH does not fund gain-of-function research in Wuhan, but Paul has insisted that Fauci is lying to Congress and even requested a criminal referral from the Department of Justice. 

In his questioning of Fauci at a recent Senate hearing, Paul cited a paper on research about bat coronaviruses and said that U.S. money had essentially gone to the hazardous and controversial research – an assertion Fauci strongly objected to. 

Fauci's National Institute for Allergy and Infectious Diseases (NIAID) did not immediately respond to Fox News' request for comment on Wednesday. But the doctor has insisted he's never lied while testifying before Congress and said if anyone is lying, it's Paul. 

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"I have never lied before the Congress, and I do not retract that statement," Fauci said. He added that the research Paul referenced was "judged by qualified staff up and down the chain as not being gain of function." 

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Fauci added: "You do not know what you are talking about quite frankly, and I want to say that officially."

In the letter, the lawmakers ask questions on specific gain-of-function research, NIAID's ties to such research abroad and how Fauci is defining "gain of function." The lawmakers ask for answers by Aug. 28.

"There is little question at this point that Dr. Fauci has misled the American public and Congress about the research that occurred at the Wuhan lab," Roy said. 

Fox News' Tyler Olson and David Rutz contributed to this report.