More 'targeted attacks' possible after ballot boxes set on fire in Washington, Oregon: Police

Authorities warned of the potential for more attacks on ballot boxes after a series of arson incidents in Oregon and Washington state.

Ballot boxes in Portland, Oregon, and Vancouver, Washington, were set on fire with incendiary devices early Monday, police said. Authorities believe the two incidents, as well as a similar incident that occurred earlier this month in Vancouver, are connected.

"Investigators believe it is very possible the suspect intends to continue these targeted attacks across the area," Portland Police Bureau spokesperson Mike Benner said at a press briefing on Wednesday.

Benner described the suspect sought in the three incidents as a white male between the ages of 30 and 40 with "balding or very short hair," a thin face and medium to thin build.

"We believe this suspect has a wealth of experience in metal fabrication and welding," Benner said.

Police are seeking one suspect in the case, Benner said.

Portland Police Chief Bob Day said that without a suspect in custody they "have to assume that there are other events that are likely to occur," but that he is encouraged by the progress in the investigation so far.

Police had previously released photos of a suspect vehicle being sought in connection with the incidents. The vehicle is believed to be a Volvo S-60 from 2001 to 2004 with a tan or light-gray interior. The vehicle has dark wheels, unpainted body trim and no front license plate, police said.

The FBI is investigating the incidents, an agency spokesperson said.

Benner said police intend to add extra patrols around ballot boxes in the wake of the attacks. Officers will also have "high visibility" in terms of their presence next week, Day said.

The most recent incidents occurred early Monday, when two ballot boxes were set on fire with incendiary devices that had been attached to them, police said.

Three ballots were damaged in the Portland incident, while fire suppressant prevented further damage, election officials said. Multnomah County Elections Director Tim Scott told ABC News that 409 ballots inside the ballot box "were undamaged" and preserved thanks to the fire suppressant.

Clark County Auditor Greg Kimsey told ABC News on Wednesday that the county has identified 475 damaged ballots in the Vancouver incident. The ballot box had a fire suppression device, which did appear to work very well, he said.

It is unclear at this time how many ballots were completely destroyed, he said.

Election officials in both states said they would ensure impacted voters have replacement ballots in time.

Monday's incident is similar to an incident that occurred on Oct. 8 in Vancouver, in which a ballot box was set on fire, police said.

The incendiary device used in that incident had "Free Gaza" and "Free Palestine" on it, two sources familiar with the ongoing investigation told ABC News.

The two subsequent devices, set off in the early hours of Monday morning in Vancouver, Washington and nearby Portland, Oregon, carried the slogan "Free Gaza," according to the sources.

One of the sources told ABC News it was unclear whether these markings reflect the views of a pro-Palestine activist -- or if it was an individual trying to manipulate existing divisions in the U.S.

ABC News' Pierre Thomas, Lucien Bruggeman and Chris Boccia contributed to this report.