BP has delayed the final efforts to plug the Macondo well in the Gulf of Mexico until September to allow the replacement of a critical piece of seabed equipment.

BP was asked to draw a plan to replace the failed blowout preventer, which sits on top of the Macondo well, with a new preventer before drilling resumes on the relief well, reports Reuters.

The relief well is 15m from its target near the bottom of the Macondo well about 4,000m beneath the seabed.

Meanwhile, Transocean, which owns the Deepwater Horizon drilling rig, said BP is withholding evidence about actions that led to the worst offshore oil spill in the US.

Nearly five million barrels of oil leaked into the Gulf, contaminating wetlands, fishing grounds and beaches from Louisiana to the Florida Panhandle.