The U.S. is accusing the oil giant BP of “gross negligence” in the 2010 explosion of an oil rig in the Gulf of Mexico that killed 11 workers.

The British oil company has already agreed to pay nearly $8 billion to settle damage claims made by fishermen and other private interests in the aftermath of the disaster. About five million barrels of crude oil spewed into waters off the southern U.S. coast two summers ago before the well was capped.

The U.S. and BP are engaged in an extended legal battle over the amount of damages the oil company owes the government for its violation of American environmental laws. The company has been pushing for a $15 billion settlement, with the U.S. holding out for substantially more.

In a court filing late last week, the U.S. said BP had engaged in a “culture of corporate recklessness.” It said the owner of the rig that exploded, Transocean, was also guilty of gross negligence.

BP said disputes about the cause of the accident have not been resolved and that it looks forward to presenting evidence when the case goes to trial in January.