WASHINGTON (AP) — Authorities on Thursday were trying to determine who sent suspicious letters, including some filled with fentanyl or other substances, to local election offices, an attack that appears to have targeted multiple states in the latest instance of threats faced by election workers around the country.

Officials in at least three states — Georgia, Oregon and Washington — reported concerns over letters targeting election workers.

Among the offices that appeared to be targeted was Fulton County in Georgia, which includes Atlanta and is the largest voting jurisdiction in one of the nation's most important presidential swing states. Authorities were working to intercept the letter. In the meantime, Secretary of State Brad Raffensperger said officials were sending the overdose-reversal drug naloxone to the office as a precaution.

"This is domestic terrorism, and it needs to be condemned by anyone that holds elected office and anyone that wants to hold elective office anywhere in America," said Raffensperger, a Republican.

There is no immediate indication that any other election office in Georgia was targeted, according to an advisory sent by the Georgia Emergency Management and Homeland Security Agency and obtained by The Associated Press.

Authorities in Lane County, Oregon, which includes the University of Oregon, were investigating a piece of mail that arrived at the local election office Wednesday. No one who came in contact with it had experienced any negative health effects, said Devon Ashbridge, spokeswoman for the Lane County Elections Office in Eugene.

The incident prompted officials to close the office and delayed an afternoon pickup of ballots. Ashbridge declined to say whether any suspicious powder was contained in the mail, referring further questions to the FBI.

"Someone attempted to terrorize our elections staff, and that's not OK," Ashbridge said. "We hope that someone will be held accountable."

On Wednesday, authorities in Washington state said four county election offices had to be evacuated as election workers were processing ballots cast in Tuesday's election, delaying vote-counting.

Election offices in Seattle's King County and in Skagit, Spokane and Pierce counties received envelopes containing powders. Local law enforcement officials said the substances in King and Spokane counties field-tested positive for fentanyl. In at least one other case, the substance was baking soda.

Tacoma Police spokesperson William Muse told The Seattle Times that a message inside the envelope received by Pierce County election workers said "something to the effect of stopping the election."

Muse said "there was no candidate that was identified. There was no religious affiliated group identified. There was no political issue identified. It was just that vague statement."

Elections offices in two Washington counties — King and Okanogan — also received suspicious envelopes while processing ballots during the August primary, and the letter sent to King County tested positive for traces of fentanyl. The county's elections director, Julie Wise, told the AP on Wednesday that letter came with a message "that certain people shouldn't have elections."

The August letters are being investigated by the U.S. Postal Inspection Service as well as the FBI. Wise said she has not received any additional information regarding the status of the investigation or whether there is a suspect.

Washington Secretary of State Steve Hobbs called the incidents in his state "acts of terrorism to threaten our elections."

A spokesperson for U.S. Department of Justice said the FBI and the postal authorities are investigating, but had no further comment.

Fentanyl, an opioid that can be 50 times as powerful as the same amount of heroin, is driving an overdose crisis deadlier than any the U.S. has ever seen as it is pressed into pills or mixed into other drugs. Briefly touching fentanyl cannot cause an overdose, and researchers have found that the risk of fatal overdose from accidental exposure is low.

It was not immediately clear how authorities came to suspect that a letter might have been sent to Georgia's biggest election office. In the advisory Thursday, state officials warned counties to take precautions when handling mail.

Raffensperger said the state alerted all 159 of its counties of the possible threat Wednesday, but believes only Fulton County is being targeted.

It's the latest disruption since the 2020 election to the office that oversees voting in and around Atlanta.

Fulton County Commission Chairman Robb Pitts, speaking at a news conference Thursday with Raffensperger, said the county's election workers had been under threat since at least when two of them were singled out following the 2020 presidential election, with then-Republican President Donald Trump, attorney Rudolph Giuliani and others falsely alleging that election workers were stuffing ballots to aid Democrats. Democrat Joe Biden narrowly won the state.

Part of the Fulton County prosecution that indicted Trump, Giuliani and 17 others includes criminal charges focusing on statements and acts made against election workers.

"There's people out there who want to do harm to our workers and want to disrupt, interrupt, the flow of democracy and free, open and transparent elections, and we're prepared for it" said Pitts, an elected Democrat.

Pitts said he believes that in 2024 Georgia's most populous county will be the "focal point" of election scrutiny.

"So this was a good trial run for us, I hate to say it," he said.

Many election offices across the United States have taken steps to increase the security of their buildings and boost protections of workers amid an onslaught of harassment and threats following the 2020 election and the false claims that it was rigged.

It's a "sad reality" that election officials are still facing threats, said David Becker, a former attorney in the Justice Department's Civil Rights Division who works with election officials through the nonprofit Center for Election Innovation & Research.

"While it may be unlikely this attack would cause serious damage, it seems clearly designed to terrorize the public servants in these offices who run elections," Becker said.

___

Associated Press writers Jeff Amy in Atlanta, Gene Johnson in Seattle, Ed Komenda in Tacoma, Washington, Jeff Amy in Atlanta and Lindsay Whitehurst contributed to this report.