A senior law enforcement official confirmed election officials in at least six states received packages, but so far none have been found to contain any actual hazardous material.

Election officials in six US states have received threatening letters, prompting investigations by the FBI and the US Postal Inspection Service, according to NBC News. A senior law enforcement official told American media that no dangerous materials have been found in any of the packages received by election officials in at least six states.

The Federal Bureau of Investigation, along with the U.S. Postal Inspection Service, are investigating suspicious packages that were delivered to election officials in several states, according to officials.