'The Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagon's remote screening facility.
When asked about the letters sent to the Pentagon, a Secret Service spokesman told CNN that "the Secret Service can confirm receipt of a suspicious envelope addressed to the President on October 1, 2018".
We have reports that two packages laced with ricin were sent to the Pentagon. The other letter was addressed to the US Navy's top officer, Admiral John Richardson, one official said.
The Secret Service spokesman said the agency was working with law enforcement partners to investigate the envelopes addressed to Trump and that all threats directed toward a Secret Service protectee "are treated seriously and fully investigated".
It is commonly used in terror plots and is found in castor beans.
Pentagon authorities found the packages during screening on Monday and turned the envelopes over to the Federal Bureau of Investigation today, officials said.
Word of the incidents in the Washington area came as authorities said two people were taken to the hospital after being exposed to a "white powdery substance" at Sen.
Ricin can be delivered in powder or pellet form, dissolved into liquid, or sprayed as a mist.
The Houston Fire Department tweeted that a hazardous materials crew is on scene at the evacuated office building. Ricin can cause death within 36 to 72 hours from exposure to an amount as small as a pinhead.
Two years later, a MS man sent letters containing ricin to President Barack Obama and a Republican senator in an elaborate attempt to frame a rival.
In June, a Wisconsin woman was accused of spreading Islamic propaganda online, including showing how to make ricin and deploy it at government facilities and water reservoirs. That same month, an Islamic extremist ricin attack planned for Germany was foiled.