"On Monday, the Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagon’s remote mail screening facility. The envelopes were taken by the FBI this morning for further analysis," Director of Defense Press Operations Col. Rob Manning said.
Defense Department spokesperson Chris Sherwood was quoted by the Military Times as saying the substance was suspected to be ricin.
READ MORE: Pentagon Says Vetting Recipients Amid Reports of US Arms on Terrorist Market
Sherwood explained the mail was addressed to an individual who works in the Defense Department, but he did not name the person.
US media reported that the two pieces of mail were addressed to Defense Secretary James Mattis and Chief of Naval Operations Adm. John Richardson.
Manning said the Federal Bureau of Investigation (FBI) is investigating the incident.