(Reuters) -A federal judge on Tuesday dismissed a negligence claim in the U.S. government's lawsuit against Berkshire Hathaway's PacifiCorp utility unit, which seeks more than $900 million in damages stemming from a 2020 wildfire in Oregon.

U.S. District Judge Karin Immergut in Portland said the government did not specify how PacifiCorp's alleged lack of care in maintaining its power lines caused the Archie Creek Fire in southwestern Oregon, dooming its "negligence per se" claim.

Negligence per se is where a defendant is assumed to breach a duty of care when violating a law, leaving only the question of whether the violation caused injury.

Immergut said relevant Oregon laws governing wildfire prevention didn't define PacifiCorp's duty of care, and it was "not enough" for the U.S. government to broadly allege that PacifiCorp's mistakes justified liability.

The government also brought claims of trespass by fire, common law nuisance and breach of license. Immergut said it can try to replead the negligence per se claim.

PacifiCorp had no immediate comment. The U.S. Department of Justice and U.S. Attorney's office in Portland did not immediately respond to requests for comment.

The Archie Creek Fire broke out on September 8, 2020 and burned 131,542 acres, including 67,074 acres of federal land, before being contained eight weeks later.

PacifiCorp also faces many private lawsuits, including proposed class actions, blaming its equipment for various Oregon wildfires.

It has lost several "mini-trials" and many more trials are expected. Through June 30, PacifiCorp recorded $2.75 billion of expected wildfire losses and said they could grow significantly.

Berkshire, based in Omaha, Nebraska, bought PacifiCorp for $5.1 billion in 2006.

At Berkshire's May 3 annual meeting, Berkshire Chairman and Chief Executive Officer Warren Buffett said "we made some mistakes" in not shielding PacifiCorp better from wildfire liability.

Vice Chairman and CEO-designate Greg Abel added that "keeping the lights on" was no longer a priority for Berkshire-owned utilities when wildfire risks grew too big.

The case is US v PacifiCorp et al, U.S. District Court, District of Oregon, No. 24-02102.