BP CEO Tony Hayward takes a first hand look at the recovery operations aboard the Discover Enterprise drill ship in the Gulf of Mexico, 55 miles (89 km) south of Venice, Louisiana on May 28, 2010. REUTERS/Sean Gardner

NEW ORLEANS (Reuters) - The U.S. government has launched a widely expected criminal and civil investigation into BP Plc's BP.L massive oil spill in the Gulf of Mexico, U.S. Attorney General Eric Holder said on Tuesday, ratcheting up the pressure on the beleaguered British oil company.

“We have begun both a criminal as well as a civil investigation as is our obligation under the law,” Holder told reporters after meeting with state and federal prosecutors in New Orleans. “Our environmental laws are very clear.”

Federal agencies, including the FBI, are participating in the probe and “if we find evidence of illegal behavior, we will be forceful in our response,” he said, adding that prosecutors had a “sufficient basis” to start a criminal probe.

After taking a tour of the oil spill, Holder said he saw “oil for miles and miles, oil that we know has already affected plant and animal life among the coast.”

The Justice Department has already demanded that the companies involved in the spill, including BP, Transocean Ltd RIGN.SRIG.N and Halliburton Co HAL.N, preserve records related to the accident.

The Justice Department will examine the companies’ actions for violations under the Clean Water Act, the Endangered Species Act, the Migratory Bird Treaty Act and the Oil Pollution Act of 1990, which can be used to hold them liable for cleanup costs and reimbursement for government efforts.

Additionally, the Justice Department could pursue other traditional charges if they find the companies made false statements or obstructed the investigation.

“As our review expands in the days ahead, we will be meticulous, we will be comprehensive, and we will be aggressive,” Holder told reporters. “We will not rest until justice is done.”