California Attorney General Kamala Harris has filed a lawsuit against the company responsible for a huge gas leak near Los Angeles.
The charges allege that the Southern California (SoCal) Gas Company violated health and safety laws by failing to report and contain leaking methane.
Ms Harris said the impact had been devastating to families in the area.
The leak in Porter Ranch began on 23 October and has forced more than 13,000 people from their homes.
It has been blamed for a variety of health issues and has been described by environmental campaigner Erin Brockovich as the worst environmental disaster in the US since 2010.
SoCal Gas spokesman Mike Mizrahi has repeatedly insisted that his company complied with all relevant state and federal regulations in the run-up to the leak.
The firm has promised that it will be plugged by the end of February and the single well in question, a depleted oil field known as SS-25, will be taken out of use.
The use of old oil and gas wells for storing natural gas is relatively common in the United States, according to industry bodies.
But the state government says that SocCal is entirely to blame for the incident.
“The impact of this unprecedented gas leak is devastating to families in our state, our environment and our efforts to combat global warming,” Ms Harris said in a statement.
“Southern California Gas Company must be held accountable.”
The lawsuit filed by the attorney general seeks unspecified civil penalties and emulates similar legal moves taken in December by the Los Angeles city attorney.
The leak has been described as the biggest in California’s history, forcing nearly 4,500 families living in the upmarket Porter Ranch area to relocate. About 1,200 more households are in the process of following them.
Repeated efforts to stop the leak by pouring liquid and mud down the stricken well have been unsuccessful. SoCal is now drilling a relief well to seal the damaged well.
Ms Brockovich has described the leak as a “BP oil spill on land”, comparing it to the Deepwater Horizon explosion in the Gulf of Mexico six years ago, in which 11 people died.
The effect of the leak on human health is contested.
SoCal Gas insists there is no evidence that it poses a long-term risk but some scientists say there are not enough data for them to be sure.
The leak in numbers
1.77 million: approximate number of cows burping for a year to produce equivalent methane
1.41 million: number of cars that would need to be added to the road to have a similar greenhouse effect in a year
13,000: number of people who have been relocated so far
Calls grow for gas facility shutdown