A series of failures by British oil giant BP and other companies led to the deadly explosion that resulted in devastating oil spill in the Gulf of Mexico, according to a key report released by the U.S. government on Wednesday.

BP, Tansocean and Halliburton "violated a number of federal offshore safety regulations," according to the report issued by the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement.

The 217-page document pinned the ultimate blame on a faulty cement drilling barrier at the Macondo well site, which investigators said failed to block oil and gas from flowing up to the rig.

"A central cause of the blowout was a failure of a cement barrier in the production casing string, a high-strength steel pipe set in a well to ensure well integrity and to allow future production," the report said.

"The failure of the cement barrier allowed hydrocarbons to flow up the wellbore, through the riser, and onto the rig, resulting in the blowout," it said.

The report concluded that the disaster was "the result of poor risk management, last minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response, and insufficient emergency bridge response training by companies and individuals responsible for drilling" at the site.

BP was "ultimately responsible" for operations at the site "in a way that ensured the safety and protection of personnel, equipment, natural resources, and the environment," according to the report.

Transocean, the owner of the Deepwater Horizon rig, was also "responsible for conducting safe operations and for protecting personnel onboard," the report said.

The investigators said that both BP and Transocean personnel on the Deepwater Horizon missed a chance to avoid the disaster when the misinterpreted unusual readings from a so-called negative pressure test of the cement barrier.

Halliburton, a BP contractor, was "responsible for conducting the cement job, and ... had certain responsibilities for monitoring the well," the report says.

The report will provide the foundation for new offshore drilling requirements as well as provide fodder for lawsuits generating from the Gulf of Mexico oil spill.

BP's Macondo well ruptured after the Deepwater Horzion oil rig, owned by Transocean and leased by BP, exploded and sank on April 20 last year, spewing up to 4.9 million barrels of oil into the Gulf of Mexico for nearly three months in the world's worst marine oil spill.