After the Pentagon inadvertently shipped live samples of anthrax to labs across nine states and a military base in South Korea, Congress is demanding answers from the Centers for Disease Control and Prevention (CDC) and the Department of Defense.

Leaders of the House Energy and Commerce Committee penned separate letters Thursday to CDC Director Dr. Tom Frieden and to Defense Secretary Ash Carter, saying the panel was "troubled" by the anthrax shipment and that it wanted briefings from the two government agencies.

"The Department's inadvertent transfer of live anthrax samples, just like similar incidents at the CDC last year, raise serious safety concerns about the sufficiency of inactivation protocols and procedures for studying dangerous pathogens," committee chair Fred Upton, R-Michigan, wrote.

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The letter, signed by a bipartisan group of members of the committee, set a deadline of June 5 for briefings by the CDC and Pentagon.

Sen. Bill Nelson, D-Florida, a member of the Senate Armed Services Committee, sent his own letter to the Secretary of the Army John McHugh, criticizing the Pentagon for its "breach of trust" and requesting a briefing for his Senate staff.

"This incident represents a serious breach of trust in the United States Army's obligation to keep our citizens and service members safe," Nelson wrote. "Moreover, the shipments to a South Korea air base weaken the United States' credibility as a global leader in chemical weapons control."

The CDC is investigating the anthrax shipments, which were reportedly sent over two months via FedEx from a U.S. Army laboratory in Utah. The samples arrived in 18 government and private laboratories in nine states and the Osan Air Base in South Korea. At this time, the CDC says, it has no reason to suspect that there is any risk to the general public, and it is scrutinizing every lab that received the DOD samples.

At the Korea base, at least 22 military personnel were exposed to the live anthrax and are receiving antibiotics as a precaution, according to Pentagon. Col. Steven H. Warren, Defense press operations director. The Pentagon also asserted that the live anthrax at the air base posed "no known risk to the general public, and no personnel have shown any signs of possible exposure."

A civilian lab in Maryland first notified the Defense Department of the live anthrax.

This latest incident isn't the first time the CDC has been criticized over its treatment of live anthrax. Last June, scientists at the CDC headquarters in Atlanta were exposed to live anthrax, prompting an investigation by the House committee.