Police believe two ballot box fires in neighboring cities in the Pacific Northwest are connected.

The FBI is investigating after drop boxes in Portland, Oregon, and nearby Vancouver, Washington, went up in flames early Monday morning.

At a press conference later on Monday, Portland Police Bureau spokesman Mike Benner said that surveillance images showed a Volvo vehicle stopping at the Portland drop box just before the fire inside the box was discovered, The Associated Press reported.

Authorities added that enough material from the incendiary devices used to start the fires at both locations was recovered to suggest that the two fires were linked. They also believe that Monday’s incidents were also connected to an earlier event, when an incendiary device was found close to a separate ballot drop box in Vancouver on Oct. 8.

In Portland, a fire suppressant inside the box protected all but three ballots, local officials said. In a statement, Multnomah County officials said that the three voters whose ballots were damaged would receive replacements.

The same protection system failed in Vancouver, which is about 10 miles across the Columbia River from Portland. Officials say hundreds of ballots were destroyed.

“Heartbreaking,” said Greg Kimsey, the auditor for Clark County in Washington, per AP. “It’s a direct attack on democracy.”

Footage of the Vancouver incident captured by ABC affiliate KATU showed heavy smoke coming from inside the box, with first responders eventually putting out the flames.

“We have multiple systems and security measures in place to ensure your ballot is safe,’’ Multnomah County Elections Director Tim Scott said. “Your elections team is working hard to make sure that every vote counts.”

“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 Steven Hobbs said in a statement.

“I strongly denounce any acts of terror that aim to disrupt lawful and fair elections in Washington state,” he added. “Despite this incident, I have complete confidence in our county elections official’s ability to keep Washington’s elections safe and secure for all voters.”

Vancouver is the biggest city in Washington’s 3rd Congressional District, where first-term Democratic Rep. Marie Gluesenkamp Perez and Republican challenger Joe Kent are facing off in what is expected to be one of the closest House races.

In a statement, Gluesenkamp Perez said she’s requesting overnight law enforcement presence at all ballot drop boxes in Clark County through Election Day.

“Southwest Washington cannot risk a single vote being lost to arson and political violence,” she said.

Last week, a United States Postal Service mail collection box was set on fire in Arizona’s Maricopa County, damaging about 20 electoral ballots inside the box.