Federal investigators are probing a series of suspicious letters containing an unknown substance that were mailed to election offices across the country, the FBI confirmed Thursday.

In an email to USA TODAY, the FBI said it is responding to each incident alongside the U.S. Postal Inspection Service and is working to identify the individual or individuals responsible for the mailings.

The letters were sent to various addresses nationwide, including Secretary of State offices and their related election offices. Some contained a substance authorities have not yet identified.

The mailings come just weeks before the Nov. 3, 2026 midterm elections, putting election administrators — including in Ohio — on heightened alert in the final stretch before voters head to the polls.

The National Association of Secretaries of State (NASS) and the National Association of State Election Directors (NASED) said in a joint statement that they are coordinating with law enforcement and have measures in place to respond to threats while “maintaining essential election operations.”

“Threats against election officials and workers have no place in our democracy,” the statement said.

The FBI said its investigation is ongoing.

Featured image: Joanna Kosinska / Unsplash, via Wikimedia Commons (CC0 public domain).