Part of Arizona State Capitol evacuated due to hazardous materials incident

PHOENIX (NBC, KYMA) - There were some tense moments at the Arizona State Capitol building in Phoenix Thursday afternoon due to a hazardous materials incident.

Part of the Capitol's Executive Tower was briefly evacuated after some type of white substance was found inside an envelope opened by staffers.

According to the Arizona Department of Public Safety, there were no reported injuries.

The FBI and U.S. Postal Inspection Service said they're investigating a series of suspicious mailings sent to various addresses nationwide Thursday, including Secretary of State offices and their related election offices.

They said some of the letters contained an unknown substance and investigators are working closely with law enforcement partners to respond to each incident, as well as to identify the individual or individuals responsible for the letters.