"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.
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.