At least two packages sent to the Pentagon are suspected of containing ricin, a Pentagon spokesman confirmed to Fox News on Tuesday.
The packages never made their way into the Pentagon, but were flagged in a mail delivery building next door, the spokesman said.
The FBI has the lead on the investigation, officials told Fox News.
“On Monday, the Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagon's remote screening facility," Col. Rob Manning said in a statement. "The envelopes were taken by the FBI this morning for further analysis. All USPS mail received at the Pentagon mail screening facility yesterday is currently under quarantine and poses no threat to Pentagon personnel.”
Ricin is a poison that can take several different forms, but as a purified powder it can be deadly. It's also one of the easiest poisons to manufacture.
In June, a Wisconsin mom was accused of spreading ISIS propaganda online -- including directing one person how to make ricin and how to deploy it at a government facility or water reservoir.
That same month, an Islamic extremist ricin attack planned for Germany was foiled.