About 35,000 people in North Carolina’s Moore County remain without power on Wednesday after the substations were damaged in what authorities described as a “targeted” attack at the weekend.

Authorities said the outages began on Saturday after one or more people drove up to the substations, breached the gates and opened fire on them. Moore County Chief Deputy Richard Maness told Newsweek on Wednesday that investigators “are working around the clock to determine” who was responsible “but are not ready to publicly identify.”

Now NewsNation has reported that a memo from federal law enforcement revealed similar attacks have taken place in other states.

“Power companies in Oregon and Washington have reported physical attacks on substations using hand tools, arson, firearms and metal chains possibly in response to an online call for attacks on critical infrastructure,” the memo says in part.

“In recent attacks, criminal actors bypassed security by cutting the fence links, lighting nearby fires, shooting equipment from a distance or throwing objects over the fence and onto equipment.”

The FBI told NewsNation that it is too early to know the motive for the attack that caused widespread outages in Moore County, but there have been similar cases in North Carolina and other states in recent months.

“While our standard practice is to decline comment on specific bulletins, the FBI routinely shares information with our law enforcement partners in order to assist in protecting the communities they serve,” an FBI spokesperson told Newsweek. “We urge the public to remain vigilant and report any suspicious activity to law enforcement.”

Ahead of November 8’s midterm elections, Newsweek documented the digital dissemination of a wide array of plots, manuals and manifestos by domestic extremists seeking to incite acts of sabotage against energy sites, especially electricity substations, across the U.S. and examples of such attacks.

Those included an act of vandalism that caused “fairly significant” damage at a transformer servicing the Keystone XL pipeline in South Dakota and a shooting that caused a chemical spill at a Pacific Gas and Electric site in California in July.

In March, thousands of customers in southern Oklahoma were reportedly left without power after bullets riddled a transformer site, causing a “major oil leak.”

On November 11, more than 12,000 people lost power in North Carolina’s Jones County after a substation owned by Carteret-Craven Electric Cooperative was damaged by criminal vandalism. The vandals damaged transformers and caused them to leak coolant oil, the company said. The investigation into that incident is ongoing, and no suspects have been identified or arrested.

In February, three men pleaded guilty to planning to recruit followers to attack substations with powerful rifles.

“The defendants believed their plan would cost the government millions of dollars and cause unrest for Americans in the region,” the Department of Justice said in a news release. “They had conversations about how the possibility of the power being out for many months could cause war, even a race war, and induce the next Great Depression.”

The Department of Homeland Security (DHS) issued a bulletin on November 30 warning that lone offenders and small groups “motivated by a range of ideological beliefs and/or personal grievances continue to pose a persistent and lethal threat.”

The bulletin said that targets of potential violence include “public gatherings, faith-based institutions, the LGBTQ community, schools, racial and religious minorities, government facilities and personnel, U.S. critical infrastructure, the media, and perceived ideological opponents.”

Newsweek reached out to the DHS for further comment.

Update 12/7/22, 8:20 a.m. ET: This article was updated with comment from Richard Maness.

Update 12/8/22, 2:20 a.m. ET: This article was updated with comment from the FBI.