Ballot boxes in Oregon and Washington were set on fire with incendiary devices early Monday in what authorities believe are related incidents, police said.

The devices used in the arson incidents were marked with the phrase “Free Gaza,” two sources familiar with the ongoing investigation told ABC News.

The ballot box fires, which occurred near the Oregon-Washington border, are also believed to be linked to a third ballot box incident that occurred earlier this month in Vancouver, Washington, police said .

The sources said the incidental device used in the first fire, on October 8, had “Free Gaza” and “Free Palestine” on it. The two subsequent devices, set off in the early hours of Monday morning in Vancouver, Washington and near Portland, Oregon, carried the slogan “Free Gaza.”

One of the sources told ABC News that it is unclear whether the markings reflect the views of a pro-Palestinian activist — or if it is someone trying to manipulate existing divisions in the US.

In the first incident reported Monday, Portland police responded to a fire at a ballot box around 3:30 a.m. local time, police said. Security from the Multnomah County Division of Elections responded and extinguished the fire, officials said.

“Our officers quickly determined that there was an incendiary device that was attached to the ballot box and that is what started this fire,” Portland Police Bureau spokesman Mike Benner said at a news conference Monday.

The bureau’s explosives disposal unit disposed of the device, police said.

The firefighter prevented further damage and protected “virtually all of the ballots,” although three were damaged, the Multnomah County Division of Elections said in a statement. press release.

Election officials said they are contacting the three affected voters so they can receive replacement ballots.

Multnomah County Elections Director Tim Scott told ABC News that 409 ballots inside the ballot box “were undamaged” and preserved thanks to the fire extinguisher.

Oregon Secretary of State LaVonne Griffin-Valade said the limited impact on ballots “demonstrates that our systems are safe and secure.”

“Make no mistake, an attack on the ballot box is an attack on our democracy and completely unacceptable,” Griffin-Valade said in a statement. “Whatever the motivation behind this incident, there is no justification for any attempt to disenfranchise voters.”

No other ballot boxes or official drop-off sites in Multnomah County were affected, the division said.

The Portland Fire Investigation Unit is investigating.

About half an hour later, around 4 a.m. local time, officers in Vancouver, Washington, responded to a report of a smoking and burning urn, police said.

“Officers arrived and found a suspicious device next to the box,” which was on fire, the Vancouver Police Department said in a statement.

The fire was extinguished and members of the Metro Explosive Disposal Unit safely collected the device, police said.

“Hundreds” of ballots are believed to have been damaged Monday, though an official number has yet to be determined, Clark County Auditor Greg Kimsey said at the news conference.

Fire extinguishers are also being installed at polling places in the county, although they don’t seem to have worked well, said Kimsey, who added that they will try to get better fire extinguishers.

The Clark County Auditor’s Office will work to ensure affected voters have replacement ballots in time, officials said.

“We take the safety of our election workers seriously and will not tolerate threats or acts of violence that seek to undermine the democratic process,” Washington Secretary of State Steve Hobbs said in a statement. “I strongly denounce any acts of terror that seek to disrupt legal and fair elections in Washington State. Despite this incident, I have full confidence in our county election official’s ability to keep Washington elections safe and secure for all voters.”

Monday’s incident is similar to an Oct. 8 incident in Vancouver in which an urn was smoking and burning with a “device” next to it, Acting Vancouver Police Chief Troy Price said during the news conference .

“We believe the incident here (in Portland) is related to the two incidents in Vancouver,” Benner said.

Police have identified a suspect vehicle, possibly a Volvo, that was captured on surveillance footage near the ballot box in Portland, Benner said.

“We know that such acts are targeted and they are intentional, and we are concerned that that intentional act is trying to affect the election process,” she said at Monday’s news conference. “We are dedicated to stopping this type of behavior and we are working on it today.”

The FBI is also investigating the incidents “to determine who is responsible,” an agency spokesman said.

Portland Gov. Tina Kotek praised the “quick response” by law enforcement and election officials.

“Voter intimidation or any criminal act to undermine the upcoming election is un-American and they will not be tolerated,” she said in a statement to X.

Both Oregon and Washington are one of several vote-by-mail states, with ballots returned by mail or to an official drop box. Washington also has voting centers open to accept ballots.