Anthrax risk for 75 scientists in US
As many as 75 people working at the US Centers for Disease Control (CDC) may have been exposed to live anthrax bacteria and are receiving treatment, the BBC reported.
The US health agency said researchers in a high-level biosecurity laboratory failed to follow proper procedures and did not inactivate the bacteria.
The exposure occurred in Atlanta at the weekend and no-one has yet shown any symptoms, the CDC has said.
The FBI has told the BBC it is helping the CDC to investigate.
"This should not have happened," Dr Paul Meechan, director of the environmental health and safety compliance told the Reuters news agency. "We're taking care of it. We will not let our people be at risk."
Dr Meechan said it was too early to determine whether the transfer was accidental or intentional.
Symptoms of anthrax exposure include skin ulcers, nausea and vomiting and fever, and can cause death if untreated.