Federal investigators are probing a string of suspicious letters sent to US election officials and congressional offices

Virginia Democrat Rep. Suhas Subramanyam disclosed on Monday that a piece of mail with a suspicious white powder had arrived at his office. The incident is the most recent in an expanding pattern, with additional lawmakers reporting they were also targeted. Federal investigators are examining letters sent to both election officials and congressional offices.

The US Postal Service is involved in the federal investigation alongside the FBI.