As many as 12 scientists may have been exposed to Ebola earlier this week in a US Centers for Disease Control and Prevention lab in Atlanta, The Washington Post reports. On Monday, scientists who were researching the disease accidentally put a sample containing the Ebola virus in a place where it was transferred to another lab on the CDC's Atlanta campus.

A person answering the media line at the CDC, who declined to be named, also declined to comment on the report.

According to the Post, a lab technician in the second lab was exposed. About a dozen people also entered the lab and may have been exposed, the Post writes. The incident was discovered Tuesday, and is being internally investigated; the lab tech who was exposed is being monitored for symptoms. Other people who may have been in the lab have been contacted, and their risk will be assessed.

"I am troubled by this incident in our Ebola research laboratory in Atlanta," said CDC Director Tom Frieden in a statement to The Washington Post. "No risk to staff is acceptable, and our efforts to improve lab safety are essential – the safety of our employees is our highest priority."