The Pentagon said the US Army's mistaken shipments of live anthrax to research laboratories were more widespread than it initially reported.
The admission prompted the US defence department to order a thorough review.
The department said 24 laboratories in 11 states and two foreign countries - South Korea and Australia - are believed to have received suspect anthrax samples.
The broadening scope of the problem suggests more extensive flaws in procedures used by the Army's Dugway Proving Ground in Utah to ensure that anthrax samples were made fully inert before shipping them to labs.
Deputy defence secretary Bob Work yesterday ordered a comprehensive review of laboratory procedures associated with inactivating anthrax.
Dugway, in a desolate stretch of the Utah desert, has been testing chemical weapons since it opened in 1942.
Earlier, the Centres for Disease Control and Prevention said suspect samples from Dugway had been sent to 18 labs in nine US states and a military base in South Korea.
Later, the Pentagon said the Army may have mistakenly sent live anthrax to a laboratory in Australia in 2008.
The CDC said the agency is testing to see which anthrax samples were live.
The results are coming in slowly, and the first full set of findings is not expected until next week.
A Wisconsin commercial laboratory, meanwhile, confirmed it was among the labs that received live anthrax spores last week.
BBI Detection of Madison, which employs fewer than 20 people, remains partially closed.
No employees have fallen ill or are in danger, and there is no danger to the public, said Jackie Lustig, a spokeswoman for Massachusetts-based Alere, which owns BBI.
CDC spokesman Jason McDonald said four people at labs in Delaware, Texas and Wisconsin were recommended to get antibiotics as a precaution, although they are not ill.
About two dozen people were being treated for possible exposure at Osan Air Base in South Korea.