Senior Capitol Hill staff received warnings on Thursday regarding multiple letters containing suspicious substances mailed to various addresses nationwide, including multiple congressional offices.

An email notice obtained by Fox News Digital sent to chiefs of staff, administrative managers, and state directors said the U.S. Postal Inspection Service, the FBI, and U.S. Capitol Police were investigating the matter.

The notice from the U.S. Senate Sergeant at Arms stated that law enforcement officials are working to intercept any additional letters before they are delivered, though it is possible that some letters may reach their destinations.

What the Right Is Saying

Fox News Digital reported that an image included in the notice showed a return address in the top-left corner for the DSA’s headquarters in New York City.

The report highlighted this specific detail from the internal notice regarding the return address on one of the envelopes.

What the Left Is Saying

The source notes that it is unclear whether the Democratic Socialists of America (DSA) had any involvement in sending the letters.

Fox News Digital reached out to the DSA for comment regarding the incident but has not heard back as of the reporting of the story.

What the Numbers Show

Fox News Digital reached out to each agency investigating the matter for comment on the nature of the substances, how many letters were sent and retrieved, and how many congressional offices could be affected.

The notice warned that all suspicious letters, packages, or substances should be treated as potentially hazardous, while authorities have not publicly identified the substances or said whether they pose a danger.

The Bottom Line

The incident comes on the 25-year anniversary when an anthrax-laced letter was opened by a staffer in then-Senate Majority Leader Tom Daschle’s office on Oct. 15, 2001.