Image caption An inquiry found the blowout preventer had snagged on a piece of drill pipe

BP is suing Transocean, the owner of the oil rig that exploded in the Gulf of Mexico last year, for $40bn (£24.37bn) in damages.

BP said safety systems on Transocean's Deepwater Horizon rig had failed.

Separately, BP also sued the maker of the rig's blowout preventer, alleging the device failed to stop the huge oil spill that followed the explosion.

Both lawsuits were filed on Wednesday on the first anniversary of the explosion, which killed 11 workers.

Overnight on 20 April 2010, Transocean's Deepwater Horizon burst into flames while drilling a well for BP.

In the months that followed, more than 200 million gallons (780 million litres) of oil flowed in the Gulf of Mexico from the well, soiling hundreds of miles of coastline in the worst US oil spill in recent history.

In federal court in New Orleans on Wednesday, BP said Swiss-based Transocean and Cameron International, the Houston company that supplied the blowout preventer (BOP), should help it pay for tens of billions of dollars in liabilities resulting from the spill, which include clean-up and compensation costs.

BP also wants the court to declare that Cameron caused or contributed to the disaster.

"The Deepwater Horizon BOP was unreasonably dangerous, and has caused and continues to cause harm, loss, injuries, and damages to BP (and others) stemming from the blowout of Macondo well" and resulting spill, the BP lawsuit said.

Cameron has filed counter-claims and defended the integrity of its products. Transocean did not immediately comment on the BP lawsuit but has also requested court judgements against BP, Cameron and others.

BP has estimated its liability at $40.9bn, but could face tens of billions more in fines and penalties.

Legal deadline

Investigators hired by the US government said last month that the blowout preventer's design was flawed, and that a piece of drill pipe trapped in the well pipe under the rig kept the blowout preventer from shearing and pinching off the well after the explosion.

In a statement supplied to the Associated Press, Cameron noted that Wednesday, the first anniversary of the disaster, was the deadline for companies to file claims against one another.

The investigators hired by the US government also said Transocean workers' actions contributed to the blowout preventer's failure.

In addition, in January a commission convened by US President Barack Obama found that BP, Transocean and Halliburton - the US company that handled the well-sealing operation ahead of the disaster - made decisions aimed at cutting costs and saving time that ultimately added to the risk of an accident.