WASHINGTON, Dec. 21 (Xinhua) -- A panel in the Democratic-controlled U.S. House on Monday issued subpoenas seeking documents from top health officials in the administration of President Donald Trump over alleged political interference with the Centers for Disease Control and prevention (CDC).

In a letter to Health and Human Services (HHS) Secretary Alex Azar and CDC Director Robert Redfield, the House Select Subcommittee on the Coronavirus Crisis said "the subpoenas were necessary because the Select Subcommittee's investigation has revealed that efforts to interfere with scientific work at CDC were far more extensive and dangerous than previously known." It said such efforts "involved numerous high-level officials at CDC and HHS."

"Documents recently obtained by the Subcommittee show that over a period of four months, as coronavirus cases and deaths rose around the country, Trump Administration appointees attempted to alter or block at least 13 scientific reports related to the virus," read the letter signed by James Clyburn, chairman of the subcommittee who, as House majority whip, is the highest-ranking African-American lawmaker in the chamber.

Clyburn said Trump administration appointees targeted reports that provided evidence of the virus's "early spread" across the country and "massive spread" this summer, which they believed sent "the wrong message" about the administration's policies.

HHS Assistant Secretary for Public Affairs Michael Caputo and his science adviser Paul Alexander spearheaded the political interference campaign, attempting to block or influence the CDC's Morbidity and Mortality Weekly Report (MMWR) for months, according to Clyburn.

Some of the reports that were targeted include one regarding hydroxychloroquine prescription trends; one on cloth face coverings; one regarding underlying medical conditions associated with the risk of severe COVID-19; and another one showing efforts to mitigate coronavirus transmission during the April 7 primary election in Milwaukee.

Caputo and Alexander have both left their posts after a series of controversies over the handling of the virus. The subcommittee revealed last week that the two officials were privately advocating for a "herd immunity" strategy to spread the coronavirus widely among Americans.

HHS officials also attempted to muzzle CDC scientists by retaliating against career employees who provided truthful information to the public, Clyburn wrote in the letter.

The subcommittee's request made on Sept. 14 for relevant documents didn't result in timely and complete response from the HHS on a voluntary basis, Clyburn said, adding that all of the documents are needed in order for the panel to "understand who in the Trump Administration was responsible for this political pressure campaign, whether it was intended to cripple the nation's coronavirus response in a misguided effort to achieve herd immunity, and what steps must be taken to end this outrageous conduct and protect American lives."