The US military said Tuesday a live sample of anthrax was inadvertently sent to a lab in Canada, after officials uncovered yet another batch of the lethal bacteria at an army facility.
The discovery raised fresh concerns about the Defense Department's handling of the deadly material and the extent of the problem involving mistaken shipments of anthrax.
Defense officials acknowledged it was unclear how many government or commercial labs could have received the vials.
The Pentagon has already admitted to blunders that include live anthrax spores being shipped to laboratories across the United States as well as to Australia and South Korea.
"We can confirm that yesterday we determined that we had shipped anthrax to Canada," Pentagon spokesman Colonel Steven Warren said.
The sample came from a larger batch or "master sample" that tested as "live," he said.
The live anthrax sample was sent to a lab in Alberta province, a defense official, speaking on condition of anonymity, told AFP.
The material had been irradiated at the US Army's Dugway Proving Ground in Utah, he said, but for some reason the bacteria was not rendered inactive as intended.
There are two other batches of live anthrax that have been found at the Dugway Proving Ground. Samples from that material have been transported to at least 28 labs in at least 12 US states. And officials said that the number is likely to go up as an internal inquiry continues.
As a precaution, 27 people were receiving preventative medical treatment, including 22 military and civilian personnel at Osan air base in South Korea.
But US officials said there was no threat posed to public health and no suspected cases of infection.
Last week, the Pentagon announced a 30-day investigation to get to the root of the problem and to examine protocols at all military labs handling anthrax. The probe is being led by Frank Kendall, undersecretary of defense for acquisition, technology and logistics.
The inquiry will look at whether the irradiation process used to inactivate anthrax bacteria was inherently flawed or whether human error was to blame, officials said.
If a technical glitch is the cause, then other army labs could be implicated and the scope of the problem would extend beyond the Dugway Proving Ground facility, officials said.