The Secret Service is investigating a suspicious envelope addressed to Trump

AP Photo/Mary Altaffer

President Donald Trump speaks during a news conference, Wednesday, Sept. 26, 2018, in New York.

• A suspicious envelope addressed to President Donald Trump was reportedly intercepted by the US Secret Service on Monday.
• The envelope did not make it inside the White House, according to a statement from the agency.
• The interception comes amid reports of at least two packages addressed to senior military officials at the Pentagon, which tested positive for ricin, a deadly poison.

The US Secret Service says it is investigating a suspicious envelope addressed to President Donald Trump.

It was not immediately clear what was inside the envelope. The Secret Service said the correspondence never made it inside the White House.

The Secret Service provided no additional details on the incident "as a matter of practice," but did acknowledge it was "working jointly with our law enforcement partners to fully investigate this matter."

"Further, all threats directed towards the President, or any Secret Service protectee, are treated seriously and fully investigated," the Secret Service statement read.

The development amid reports of at least two packages addressed to senior military officials at the Pentagon, which tested positive for ricin, according to a CNN report. The Pentagon's Force Protection Agency detected "a suspicious substance" as it screened its mail at a remote facility, a Pentagon spokesman said to Business Insider on Tuesday.

The packages, which were addressed to Defense Secretary James Mattis and Chief of Naval Operations, Adm. John Richardson, were "under quarantine" and posed no threat to the Pentagon's personnel, according to the spokesman.

Ricin, a chemical defined by the Centers for Disease Control and Prevention as a "stable substance under normal conditions," could be in a powder, mist, or pellet form. Ricin is found in castor beans and can cause injury if chewed or swallowed, according to the CDC.