House Republicans are accusing the Biden administration of obstructing their investigation into COVID-19's origins, arguing in a new letter that the Department of Health and Human Services (HHS) is hiding information from them.

"Rather than be transparent with committee Republicans, HHS and NIH [National Institutes of Health] have chosen to hide, obfuscate, and shield the truth," reads Wednesday's letter. 

"This stonewalling is particularly troubling considering NIH’s direct involvement in responding to the COVID-19 pandemic, and the agency’s policy or practice to destroy potentially pertinent documents related to grant making decisions."

Oversight

House Oversight and Reform Committee Ranking Member James Comer (R-KY) speaks during a House Oversight and Reform Committee hearing titled The Capitol Insurrection: Unexplained Delays and Unanswered Questions, on Capitol Hill on May 12, 2021 in Washington, D.C. (Jonathan Ernst-Pool)

The letter was signed by 18 members of the House of Representatives, including Oversight Committee Ranking Member James Comer, R-Ky. It was addressed to HHS Secretary Xavier Becerra and NIH acting Director Dr. Lawrence Tabak.

FAUCI'S GAIN-OF-FUNCTION RESEARCH AND WHY I'LL CONTINUE TO HOLD HIM, HIS ALLIES ACCOUNTABLE

House Republicans had requested HHS provide documents related to the 2014 NIH grant awarded to EcoHealth Alliance, which conducted research with the Wuhan Institute of Virology. That May 2021 request was followed by a letter in July 2021.

Anthony Fauci

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, speaks during the daily briefing at the White House in Washington, Wednesday, Dec. 1, 2021. (AP Photo/Susan Walsh)

"By continuing to refuse to cooperate with our request, HHS and NIH are choosing to hide information that will help inform the origins of the ongoing pandemic, prevent future pandemics, strengthen the United States’ national security posture, and restore confidence in our public health experts and infrastructure," Wednesday's letter reads. 

Wuhan

Security personnel gather near the entrance of the Wuhan Institute of Virology during a visit by the World Health Organization team in Wuhan in China's Hubei province on Wednesday, Feb. 3, 2021. (AP Photo/Ng Han Guan)

"The agencies’ continued obstruction is likely to cause irreparable harm to the credibility of these institutions. By providing the requested documents and information, HHS and NIH will have the opportunity to help our country move forward in a positive, transparent direction following the COVID-19 pandemic."

HHS did not immediately respond to Fox News Digital's request for comment.

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The letter adds to mounting scrutiny of HHS and Dr. Anthony Fauci, who has spearheaded the government's response to the coronavirus. 

Wednesday's letter reiterates House Republicans' previous request with added specificity and asks HHS for a response by Feb. 16.