A U.S. military laboratory shipped samples of live anthrax to 51 facilities in 17 states, the District of Columbia and three foreign countries, USA Today reported based on Pentagon officials' statements.

The figure, which includes more than twice as many labs as previously indicated, is the result of an internal investigation led by Deputy Defense Secretary Robert Work, who noted that "we expect this number may rise" further.

In what the Daily Beast called an "anguished briefing," Pentagon officials on Wednesday tried to reassure the public that it was not in danger. The department and the Atlanta-based Centers for Disease Control were conducting a thorough review.

Before it shipped out the anthrax samples, military labs had conducted quality-assurance tests that were accepted practice by the scientific community, officials further insisted. But those samples are not supposed to be alive when they are shipped, and strict procedures are in place to prevent that from accidentally happening, the Daily Beast detailed.

Cmdr. Franca Jones, the director of medical programs for the Pentagon's chemical and biological defense programs, told the website that experts take a 5-percent sample from the prepared anthrax and test it in order to then issue a "death certificate" for the spores.

But Richard Ebright, a professor of chemistry and chemical biology at Rutgers University, said that many private labs test a sample as high as 20 percent. "The less you take, the less reliable it is," Ebright noted.

Contact with live anthrax can be fatal, and the spores have triggered alarms at other agencies, as well, the New York Times recalled.

Last June, officials said dozens of employees of the Centers for Disease Control and Prevention might have been exposed to live anthrax, the newspaper detailed. And the federal health service has also had a transport-related mishap: A CDC lab accidentally contaminated a relatively benign flu sample with a dangerous H5N1 bird flu strain and then shipped it to an Agriculture Department facility.

In another incident listed by the New York Times, vials of smallpox and other infectious agents were found last July on the campus of the National Institutes of Health, where they had been stored and "apparently forgotten" for about 50 years.