EXCLUSIVE: Sen. Marsha Blackburn, R-Tenn., on Tuesday urged President Biden to use his leadership to ensure the investigation into the origins of the coronavirus in Wuhan, China, by the World Health Organization (WHO) is free from conflict of interest -- amid continued concern over the probe by the controversial body.

"I urge you to use your leadership to ensure investigations by the World Health Organization are free from conflict of interest," Blackburn said in a letter to Biden, obtained by Fox News.

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Blackburn noted that while the COVID pandemic had taken a toll on American life and the economy, "the investigation into the origins of the pandemic are not complete."

The World Health Organization recently sent a team of investigators to Wuhan, where the outbreak was believed to have originated. The team was there for a month, visiting markets and other key locations -- although the visit is seen as only the first step of the investigation.

But the probe has been dogged by reports of the secretive Chinese regime withholding information -- although that has been denied by some team members -- and concerns about potential conflicts of interest.

A recent Wall Street Journal article raised concerns about one member on the WHO team whose organization had administered more than $100 million in federal grants to fund overseas work and experiments -- including work by the Wuhan lab where the outbreak is believed to have started.

Early on in the pandemic, when little was known of the virus, he reportedly dismissed the claim that the virus was created in a lab as a conspiracy theory -- although his spokesman told the Journal he was supporting scientists at a time they were receiving online harassment.

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"Concerns have been raised about the lack of transparency of the events that took place at the outbreak started in Wuhan, China," Blackburn wrote to Biden. "In addition, concerns have been raised regarding the manner in which World Health Organization investigators were chosen to study the outbreak and some of the conflicts of interest that exist in those investigators."

Some of those concerns are shared by the Biden administration, which has stopped the former Trump administration’s withdrawal from the U.N. body. National Security Adviser Jake Sullivan said the administration had "deep concerns about the way in which the early findings of the COVID-19 investigation were communicated and questions about the process used to reach them."

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"It is imperative that this report be independent, with expert findings free from intervention or alteration by the Chinese government," he said.

However, the Biden administration has so far not addressed the concerns about a conflict of interest. Blackburn urges Biden to "use your leadership to ensure the ongoing investigation of the COVID-19 pandemic origin be free from conflict of interest."

"WHO should be required to have independent investigators to conduct this study. Who should not include researchers with conflicts of interest or with a lack of experience in forensic investigation," she said in the letter.

"We owe this to the over 500,000 Americans who have died from this disease, to their families, and to future Americans who face possible pandemics," she wrote.

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Blackburn has consistently called for a tough stance against Beijing. She repeated that call when speaking to Fox News at the Conservative Political Action Conference (CPAC) last week in Orlando.

"And we need to be very specific with China that we know they're our adversary, they are not our ally and we need to bring our manufacturing jobs back from China, we need to end these Confucius Institutes that are on our college campuses and we need to make sure China is held accountable for sending us COVID-19," she said.

The Associated Press contributed to this report.