Curfew in the U.S. due to power plant attack

Tens of thousands of homes and businesses in North Carolina have been without power for four days as authorities investigate what they describe as an orchestrated shooting attack that disabled two substations.

North Carolina Governor Roy Cooper said there needs to be "a serious national conversation" about protecting critical infrastructure in the wake of the attack.

Duke Energy Corp, which provides power to the area, reported that more than 35,000 customers remain without power in Moore County, where the FBI and the U.S. Department of Energy along with local and state law enforcement agencies are investigating.

"Investigators left no stone unturned. This was a malicious criminal attack on the entire community that plunged tens of thousands of people into darkness. It is unacceptable to have so many people without power for so long. It was clear that they knew how to cause significant damage and that they could do it at this substation, so we need to reevaluate the situation," Cooper told CNN.

"The reason for the wave of damage is unclear," Moore County Sheriff Ronnie Fields said.

Due to the power outages, schools remained closed from the first business day of the week, with temperatures dropping below freezing at night.

"The incidents are being investigated by local, state and federal law enforcement agencies, including the FBI," Fields added.

About 64% of Moore County electricity customers remain without power as of Sunday night, in a mostly rural area about 90 miles east of Charlotte.

It was "a targeted attack. It was not random," Fields warned.

Utility workers found broken doors and evidence of damage, from shots fired at equipment.

The outages could extend into Thursday, Duke Energy spokesman Jeff Brooks said, because of the extent of the damage.