LAS VEGAS (KLAS) — Federal and state law enforcement agencies were investigating letters mailed to election officials in several states, including Nevada, which contained fentanyl, two sources said.

An FBI spokesperson in Las Vegas said the letters were sent to ballot counting centers in several states.

In several cases, preliminary tests showed the presence of fentanyl in the letters, sources said. The illicit drug is 50-to-100 times more potent than heroin.

In addition to Nevada, the letters were sent to California, Georgia, Oregon and Washington.

There was no indication Thursday that any election official in Nevada was injured from the letters.

“The FBI, along with our law enforcement partners, responded to multiple incidents involving suspicious letters sent to ballot counting centers in several states. As these are ongoing matters, we do not have any further comment, but the public can be assured that law enforcement will continue to keep the public’s safety as its top priority,” according to Sandy Breault, in the Las Vegas Field Office.

“The FBI would also like to remind everyone to exercise care in handling mail, especially from unrecognized senders. If you see something suspicious, please contact law enforcement immediately,” Breault said.

A nationwide investigation is looking into the matter, a statement on the Nevada Secretary of State’s website indicated Thursday afternoon.

“We are aware of the reports of suspicious letters addressed to election offices in multiple states, including Nevada, and we are in communication and coordinating with federal, state and local agencies, including the Federal Bureau of Investigation, the United States Postal Service, the Nevada Department of Public Safety and the Office of the Governor. As this is an ongoing investigation, we have no further comment at this time.”