WASHINGTON (AP) — Authorities at the Pentagon found at least two packages suspected of containing ricin, a poison made from castor beans, a spokesman said on Tuesday.

Pentagon spokesman Chris Sherwood said the FBI was investigating and few details were available. He said the packages had been found on Monday at a delivery screening facility that is on the Pentagon grounds but not inside the main building that includes the offices of the defense secretary.

Sherwood said the packages were addressed to a person at the Pentagon. He would not reveal the name.

Another Pentagon spokesman, Col. Rob Manning, said all U.S. Postal Service mail received at the screening facility on Monday is under quarantine and “poses no threat to Pentagon personnel.”

Ricin is part of the waste “mash” produced when castor oil is made. According to the Centers for Disease Control and Prevention, if it is made into a partially purified material or refined, ricin can be used as a weapon capable of causing death under certain circumstances.