The Secret Service is investigating a letter addressed to President Donald Trump that may have contained the deadly poison ricin, according to a CNN report Tuesday evening.

WATCH:

“The FBI is investigating three suspicious envelopes sent to the President of the United States, as well as to the Pentagon. Two of the letters have initially already been tested and they are positive for the deadly poison ricin. The letter to the president is suspected of containing ricin, as well,” CNN anchor Wolf Blitzer stated.

“The Secret Service is confirming that a suspicious envelope was received addressed to President Trump,” said Barbara Starr, CNN’s Pentagon correspondent. “There are indications they suspect — suspect only at this point — it may have contained ricin. Additional testing will have to be completed. The Secret Service [is] being very close about the details, not saying exactly where that letter was received.”

The day prior, two letters addressed to James Mattis and Admiral John Richardson containing the same poison were discovered at the Pentagon.

As Starr explained, “Yesterday, two letters received here at the Pentagon, one addressed to Defense Secretary James Mattis, one addressed to the Chief of Naval Operations, Admiral John Richardson, the head of the U.S. Navy. Both of those letters also initially testing positive for what they believe might be ricin.”

When asked if the letters appear to be connected, she said, “Well, some people are saying that they are concerned, some federal officials are saying they are concerned that there is a connection.”

The FBI confirmed earlier on Tuesday that they took possession of the envelopes that were sent to the Pentagon. (RELATED: Mail Sent To Mattis Tests Positive For Ricin)

Additionally, two people were taken to the hospital Tuesday after a powdery substance was found in mail addressed to Sen. Ted Cruz’s Houston campaign office earlier in the day, as well. The substance, however, turned out to be harmless.

Follow Mike on Twitter.