BP will proceed with a relief well to kill its blown-out Gulf of Mexico well, the top US spill official said on Friday.

Engineers monitoring BP’s damaged well in the Gulf of Mexico detected seepage on the ocean floor that could mean problems with the cap.

BP’s US chief faces accusations in Congress that the energy giant caused the worst oil spill in US history with a calculated strategy to cut costs.

An oil slick from a blown-out well in the Gulf of Mexico is expected to reach a wildlife reserve at the mouth of the Mississippi River on Thursday.