U.S. Attorney General Eric Holder on Wednesday announced the government is suing British oil giant BP and eight others for the massive Gulf of Mexico oil spill earlier this year, seeking unlimited damages.

Besides BP, which leased the Deepwater Horizon rig that exploded on April 20, creating the worst offshore oil spill disaster in U.S. history, defendants in the suit also include the rig's owner Transocean Ltd, Anadarko Petroleum Corp, Mitsui & Co Ltd unit MOEX and BP's insurer Lloyds of London.

The lawsuit demands the companies be held liable without limitation under the Oil Pollution Act for all removal costs and damage caused by the oil spill, including damage to natural resources. The lawsuit also seeks civil penalties under the Clean Water Act.

Holder said the companies were in "violations of safety and operational regulations," and "we intend to prove these violations caused or contributed to the massive oil spill."

The lawsuit alleges that safety and operating regulations were violated in the period leading up to the April 20 explosion.

The lawsuit was filed earlier in a federal court in New Orleans. Thousands of individuals and small businesses have already filed suits against BP. U.S. media outlets counted more than 300 suits have been spawned by the spill and consolidated in federal court in New Orleans.

The oil spill in the Gulf of Mexico following the explosion at the rig lasted for three months, with its damage yet to be fully known months after the well was capped, according to the lawsuit.

The spill caused extensive damage to marine and wildlife habitat in and around the Gulf of Mexico. Local fishing and tourism industries were devastated. Federal, state and local governments as well as businesses spent billions in cleaning up the spill and the recovery effort.