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Ahead of possible unrest due to Tuesday's presidential election, the National Guard is on standby in several states as a precaution, including Washington state and Oregon, where hundreds of ballots were damaged or destroyed after at least three ballot boxes were recently set on fire, officials say.

Almost all of the ballots set on fire Monday were in a mailbox in Vancouver, Washington, while most of the ballots in a mailbox in Portland, Oregon, survived the fire that same day, election officials said. The incidents are believed to be related to a third fire on October 8, also in Vancouver. Portland police released a physical description of a suspect but said they have not identified him.

Washington Gov. Jay Inslee addressed the ballot box fires in a press release Friday announcing the National Guard's standby status: “Specified cases of election-related unrest have already occurred in the southwest region of Washington state.”

Inslee did not disclose how many troops would be activated Tuesday, but said they would be available to support law enforcement Monday through Thursday, according to the news release.

The US Department of Homeland Security warned that threats to “election infrastructure” remained high, Inslee added.

“Based on general and specific information and concerns about the possibility of violence or other unlawful activity related to the 2024 general election, I want to ensure that we are fully prepared to respond to any possible further unrest,” Inslee said.

In Oregon, Gov. Tina Kotek said in a statement Friday that the National Guard was ready as political leaders called for peaceful protests, according to CNN affiliate KTVZ.

“The governor’s office is closely monitoring and coordinating with local, state and federal authorities to ensure Oregon voters can cast their ballot safely,” the statement said.

Although there is “no current information indicating unrest,” Portland Mayor Ted Wheeler said, according to KTVZ, “there is a lot of uncertainty and tension in our community.”

Oregon State Police, along with the Oregon Department of Emergency Management, are also coordinating law enforcement in Portland, according to KTVZ.

Portland's unified command, which includes the city's police force, is increasing staffing on Tuesday “as a precautionary measure,” according to a news release.

In 2020, former Oregon Gov. Kate Brown put the National Guard on standby for 48 hours around Election Day and activated a unified command of state troopers, sheriff's deputies and Portland police to handle any protests, according to the Associated Press .

In recent years, the National Guard has been deployed in several states to largely assist with cybersecurity threats during elections. The Colorado National Guard's Cyber ​​Task Force was activated this year – a practice that has been in place since 2018 – to protect election “infrastructure,” the Colorado Secretary of State's Office said in a statement last month.

Nevada Gov. Joe Lombardo also announced this week that 60 National Guard troops were on standby “in preparation for a safe and smooth Election Day.”

“This decision, which reflects the state’s routine preparation for past elections, was made in consultation with election officials and state leaders,” Lombardo said in a statement. “This is one of many proactive steps the state is taking to ensure every possible resource is in place to respond in a timely manner to challenges as they arise.”

The activation will support state and local resources on Election Day, the statement said.

Preparations are also underway in Washington, D.C., where more than 3,000 police officers will work 12-hour shifts, Police Chief Pamela A. Smith said in a news conference Tuesday.

To ensure security, police chiefs across the United States are making unprecedented plans for Election Day and the weeks that follow. Since the January 6, 2021 insurrection at the U.S. Capitol that delayed the certification of the last presidential election, the issue has become urgent for law enforcement.

Three law enforcement associations representing agencies from across the country — the Major County Sheriffs of America, the National Sheriffs' Association and the Major Cities Chiefs Association — said in a joint statement last month that authorities have been preparing for more than a year and a half in Ahead of the election and urged citizens to also remain vigilant.

“As always, the associations encourage the public to speak out if they observe anything suspicious or unusual related to electoral activities,” the statement said. “When you 'see something, say something' and let law enforcement investigate suspicious circumstances or incidents and determine the outcome.”

CNN's Chris Boyette, Shimon Prokupecz and Meridith Edwards contributed to this report.