The Obama administration...launched a legal battle against BP Plc and its partners by suing them for the worst offshore oil spill in U.S. history, which could cost the companies billions of dollars..."While today's civil action marks a critical step forward, it is not a final step," U.S. Attorney General Eric Holder told reporters at a news conference. "Both our criminal and civil investigations are continuing..." he said...The suit...was filed in a New Orleans federal court which is considering private lawsuits against BP and the others for the spill...In response to the lawsuit, BP said it is "solely a statement of the government's allegations and does not in any manner constitute any finding of liability or any judicial finding that the allegations have merit."..."BP will answer the government's allegations in a timely manner and will continue to cooperate with all government investigations and inquiries," the company said...The lawsuit accused the companies of violating safety and operating regulations in the period leading up to the disaster...After the lawsuit was filed, [BP's] partners said the blame and liability laid squarely on BP..."The responsibility for hydrocarbons discharged from a well lies solely with its owner and operator," Transocean said in a statement...[also refers to Anadarko, Cameron, Exxon, Halliburton, MOEX, Mitsui, QBE Underwriting/Lloyd's, Lloyds of London]