Swiss-based oil rig owner Transocean is one of several firms being sued by the US Justice Department for economic and environmental damage in the Gulf of Mexico spill.
It is seen as a first step by the US authorities to gain billions of dollars in compensation for the disaster, in which 11 people died.
“The department’s focus on investigating this disaster and preventing future [spills] is not over,” Attorney General Eric Holder said during a news conference in Washington. “Both our civil and criminal investigations are ongoing.”
The move sent the share price of Transocean falling at the stock exchange in Zurich. By Thursday evening, it had declined by 3.37 per cent to SFr67.45 ($69.74).
The federal lawsuit, filed in New Orleans, accuses BP and eight other firms of violating federal regulations and failing to prevent the April 20 explosion and fire, which destroyed the Deepwater Horizon offshore drilling rig, owned by Transocean.
Based in Zug in central Switzerland, Transocean has disputed the allegations and insisted it should not be held liable.
Brian Kennedy, a spokesman for Transocean, which leased the Deepwater Horizon rig to BP, said: “Responsibility for oil and natural gas discharged from a well lies solely with the well’s owner and operator...Transocean is indemnified in this matter.”
swissinfo.ch and agencies