The emails, obtained by the Daily Caller News Foundation, date back to 2012, when Fauci was defending experiments that made a highly dangerous strain of bird flu transmissible through the air.

Dutch virologist Ron Fouchier conducted the experiments with funding from Fauci's National Institute of Allergy and Infectious Diseases (NIAID).

Fouchier described the resulting virus as "probably one of the most dangerous viruses you can make."

The experiments triggered debate over whether the potential benefits of gain-of-function research justified the potentially catastrophic consequences of an accidental laboratory escape.

New York Times science writer Phil Boffey was among those sounding the alarm, warning of an "engineered doomsday" capable of killing "hundreds of millions of people."

Boffey also suggested that the NIH had its own reputation at stake because it had financed the experiments.

That criticism apparently irritated Fauci.

"Phil Boffey is really off base here," Fauci wrote to then-NIH Director Francis Collins on March 4, 2012. "He is acting like a mischievous guy."

The following morning, Fauci complained about the article to his subordinate.

"Clearly, people are getting to Phil Boffey and he is swallowing it," he wrote.

Fauci then gave an explicit instruction concerning the correspondence.

"Please delete this e-mail and then delete from the deleted file," Fauci wrote from his government email account.

The revelation raises further questions about Fauci's handling of federal records.

Sen. Rand Paul (R-KY) has previously highlighted two other instances in which Fauci allegedly sought to delete government communications.