The U.S. Secret Service said Tuesday that it intercepted a suspicious envelope addressed to President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE a day earlier, one of at least three reported instances of suspicious mail being sent to government- or political-related offices in recent days.

The Secret Service confirmed to The Hill that the suspicious envelope was not received at the White House, nor did it enter the building. The organization did not comment on whether the suspicious letter at the White House may be related to one at the Pentagon, but said it is working with law enforcement partners to investigate the matter.

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The Secret Service statement came hours after Pentagon spokesman Col. Rob Manning said in a statement that staff there detected a suspicious substance in multiple letters while screening mail on Monday.

CNN first reported that the letters tested positive for the poisonous substance ricin. No illnesses were reported from exposure to the toxin.

Also on Tuesday, two people were taken to the hospital after they were exposed to a piece of mail sent to Sen. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE's (R-Texas) Houston-based campaign headquarters containing a white powdery substance.

A hazmat team and firefighters from the Houston Fire Department responded to the incident when Cruz's campaign staff reported the mail to authorities after opening it.

A campaign spokeswoman said Cruz's team couldn't say what the substance was.