The Pentagon received two pieces of mail laced with ricin Monday, prompting officials to investigate.

“On Monday, the Pentagon Force Protection Agency detected a suspicious substance during mail screening at the Pentagons remote screening facility,” Pentagon spokesperson Col. Rob Manning said in a statement, CNN reported Tuesday. “The envelopes were taken by the FBI this morning for further analysis.”

Ricin is an extremely potent toxin derived from the castor bean. A tiny dose, equivalent to a few grains of salt, can kill a human. The toxin can be distributed as a powder, pellet, mist or acid.

The mail was sent to Secretary of Defense James Mattis and to Admiral John Richardson, the Chief of Naval Operations, according to a defense official.

No mail enters the Pentagon before it is screened at the buildings screening facility. All of Mondays mail is currently being quarantined.

The FBI also made a statement about the toxic mail: “On Tuesday, October, 2, 2018, in coordination with the Pentagon Force Protection Agency, FBI Special Agents took possession of two suspicious envelopes that had been screened at the Pentagon mail facility. Those envelopes are currently undergoing further testing.”

A ricin-laced envelope was intercepted at the U.S. Capitols mail facility in April 2013. The letter was addressed to Mississippi Republican Sen. Roger Wickers office. Poison ricin letters have also been sent to former president Barack Obama and other leading politicians. (RELATED: Six Syrian Refugees Detained For Allegedly Planning Christmas Attack In Germany)

German police arrested a 29-year-old Tunisian immigrant in Cologne in June for planning to use the toxin in a bomb, according to the German state prosecutors office. French authorities also arrested an Egyptian–born student in Paris in May over possible involvement in building ricin-based poisons. (RELATED: Paris Attacker Is Chechnya-Born French Citizen Known To Authorities)

Two people were whisked to the hospital Tuesday after a powdery substance was found in mail sent to Sen. Ted Cruzs Houston campaign office.

Two people were taken to the hospital after apparently being exposed to a white powdery substance in an office building at 3200 SW Fwy. The 9th floor of the Phoenix Tower has been evacuated as HFD HazMat is responding to the scene working to determine the nature of the substance.

— Houston Fire Dept (@HoustonFire) October 2, 2018

The latest reports indicate the substance sent to Cruzs office was harmless.

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