A Centers for Disease Control and Prevention lab technician may have been exposed to the Ebola virus earlier this week following a mishap at an Atlanta facility, the agency said Wednesday afternoon.

The accident, which occurred on Tuesday, happened when two sets of vials in the laboratory -- one containing an active sample of the deadly virus, one containing an inactive sample -- got mixed up, officials said. The experiment material was on a sealed plate, but it wasn't supposed to be moved into the lab the technician was working in.

The technician who processed "a small amount of material" from the experiment has been assessed and will be monitored for 21 days, although he was not showing any symptoms of the illness as of Wednesday.

The CDC said there was "no possible exposure" outside the laboratory and "no exposure or risk" to the public.

The possible exposure is under internal investigation and has been reported to Secretary of Health and Human Services Sylvia Burwell, a CDC spokeswoman said. Additional employees have been notified, but none has required monitoring.

"I am troubled by this incident in our Ebola research laboratory in Atlanta," CDC Director Tom Frieden said. "We are monitoring the health of one technician who could possibly have been exposed and I have directed that there be a full review of every aspect of the incident and that CDC take all necessary measures."

Earlier Wednesday afternoon, The Washington Post reported that as many as a dozen scientists at the Atlanta facility may have been exposed, though FoxNews.com was unable to immediately corroborate the report. A spokeswoman for the agency told FoxNews.com that she had no information immediately available.

In June, at least 52 workers at the CDC took antibiotics as a precaution because a lab safety problem was thought to have exposed them to anthrax.

Fox News' John Roberts, FoxNews.com's Karl de Vries and The Associated Press contributed to this report.