A shooting that damaged two power substations in a North Carolina county, leaving thousands of homes without power, has been deemed a "targeted" attack, as officials warn of threats to the nationwide infrastructure.
Days before the attack, the Department of Homeland Security issued a bulletin through its National Terrorism Advisory System warning that the "United States remains in a heightened threat environment" and "lone offenders and small groups" may commit acts of violence on various targets, including critical infrastructure in the country.
The bulletin follows a report made in January, in which the DHS warned that domestic extremists have been developing "credible, specific plans" to attack electricity infrastructure since at least 2020.
Extremists "adhering to a range of ideologies will likely continue to plot and encourage physical attacks against electrical infrastructure," the report warned.
More than 6,400 power plants and 450,000 miles of transmission lines run across the country.
After the two electrical substations in Moore County, North Carolina, were shot up, thousands of utility customers had no power for several days. At the height of the outage, more than 45,000 customers were left in the dark amid freezing temperatures.
"It was targeted; it wasn't random," said Moore County Sheriff Ronnie Fields at a news conference Sunday.
It was the latest of a number threats to the power grid over the last decade.
In 2013, the Federal Energy Regulatory Commission ordered grid operators to increase security following a sniper attack on a California power substation. The case remains unsolved but caused power outages and millions of people were advised to conserve energy.
A Utah man was arrested in 2016 and was later sentenced to federal prison after he used a rifle to shoot the cooling fins on a substation, which caused the substation to overheat and fail. The man had planned to attack other substations to take down power in portions of the western United States, court documents said.
'IT WASN'T RANDOM': Outages in North Carolina county could last days after 'targeted' attack on substations
What happened in Moore County?
The outages began at about 7 p.m. Saturday in Carthage, North Carolina, after one or more people "opened fire" at two substations, according to Fields. Outages then spread through portions of central and southern Moore County, Fields said.
Duke Energy, a North Carolina power company, said it expects to have power back in Moore County on Wednesday just before midnight. The company initially estimated that power would be restored by Thursday morning.
About 35,000 customers were still without power Tuesday, a decrease from the height of the outage on Saturday where more than 45,000 customers lost power, the company added.
Duke Energy has been working to replace and repair "large and vital pieces of equipment," the company said Tuesday afternoon. The company has also implemented "rolling power-ups" to give power in two- to three-hour waves to some customers in the northern part of Moore County, according to Sam Stephenson, a power delivery specialist for Duke Energy.
Moore County has a population of about 100,000 people and is about an hour's drive southwest of Raleigh, North Carolina.
GRAPHICS: Locations of North Carolina power substations attacked by gunfire
'A wake-up call to provide better security'
While investigators have not released a motive or identified a suspect, officials have called for improvements in critical infrastructure.
Mike Causey, the North Carolina insurance commissioner and state fire marshal, called the attack "a wake-up call to provide better security at our power substations."
North Carolina Gov. Roy Cooper addressed short-term and long-term plans for the county early Tuesday and called for an assessment of the state's critical infrastructure during the monthly Council of State meeting, which includes how to prevent future attacks and bolstering security.
The state has sent generators to the county and is helping feed residents, Cooper said during the meeting. Substations nearby are also being closely monitored by law enforcement.
"This seemed to be too easy," Cooper said after the meeting. "People knew what they were doing to disable the substation, and for that much damage to be caused - causing so much problem, economic loss, safety challenges to so many people for so long."
'IT COULD HAPPEN TOMORROW': Experts know disaster upon disaster looms for West Coast
Residents still in the dark
Moore County residents without power faced below-freezing temperatures overnight but milder temperatures are expected for Tuesday nightand Wednesday, according to the National Weather Service.
Businesses and all county schools remained closed Tuesday. Moore County Schools said all schools will be closed Wednesday and Thursday.
A curfew remains in place from 9 p.m. to 5 a.m. and traffic lights in the area are still out. Meals and water have been distributed to residents at various businesses and the local food bank.
An emergency shelter at the county sports complex in Carthage had about 54 people on Monday night, an increase from 19 people the night before. Many other residents have stopped by the shelter for food, warmth, showers or to charge their devices.
Bryan Phillips, director of Moore County Public Safety, said officials were working to determine if a death in the county was related to a medical condition or to the power outage. The resident who died was without power, he said.
Contributing: The Fayetteville Observer; The Associated Press
This article originally appeared on USA TODAY: North Carolina 'targeted' outage attack latest in power grid threats