Rep. Adam Smith joins lawmakers who received letter with 'suspicious substance'

Reports suggest there are over 100 letters circulating in the U.S. mail system.

Washington State Democratic Congressman Adam Smith received a "suspicious letter containing a powdery substance" on Monday, according to a statement from the congressman's office, making the lawmaker the latest in a growing list of politicians who have received similar letters.

"Earlier today, my district office received a suspicious letter containing a powdery substance, like others sent to Congressional offices across the country," Smith said in a statement to ABC News. "My staff has been safely evacuated, and I thank the Kent Police Department and the Renton Fire Department for their quick action."

At Smith's office in Kent, Washington, hazmat units from both Puget Sound Regional Fire Authority and Renton Regional Fire Authority, along with Puget Sound Fire's battalion chief, were dispatched at 2:45 p.m. local time, according to Puget Sound Fire Division Chief Pat Pawlak.

In recent days, several other lawmakers across the country have received suspicious letters, including Senate Minority Leader Chuck Schumer and Democratic senators Chris Murphy, Kirsten Gillibrand and Lisa Blunt Rochester, according to previous ABC reporting.

ABC previously reported that preliminary information suggests there are over 100 letters circulating in the US mail system that apparently contain white powder, according to law enforcement sources.

It's unclear if this incident is connected to the other letters, but in a statement, the FBI told ABC News: "The FBI and U.S. Postal Inspection Service are investigating a series of suspicious mailings sent to various addresses nationwide, including Secretary of State offices and their related election offices."

"Some of the letters contained an unknown substance, and we are working closely with our law enforcement partners to respond to each incident," the FBI said.