WASHINGTON: Hackers breached at least a dozen US power plants in attacks in May and June, US media report, citing intelligence officials.
The targets included the Wolf Creek nuclear facility in Kansas, according to several reports.
An urgent Department of Homeland Security (DHS) report indicated a foreign power, possibly Russia, was responsible, US newspaper said.
The DHS document carried the second-highest threat rating, the US newspaper said.
Wolf Creek Nuclear Operating Corp declined to say if the plant was hacked but said there had been "no operational impact" at the plant.
US investigators accused Russia-based hackers of being behind a 2015 attack that caused blackouts across Ukraine.
Hacking is a tool increasingly deployed by nation states to infiltrate foreign industrial networks. The US and Israel reportedly used the now-infamous Stuxnet worm in an attempt to damage an Iranian nuclear facility.
The worm attacked the facility's nuclear centrifuges by overriding the system and instructing them to spin much faster than intended, reportedly causing severe physical damage.