Updated

Federal officials said late Friday they have approved a joint plan from BP and Transocean to identify the source of a sheen in the Gulf Of Mexico associated with the 2010 Deepwater Horizon oil spill.

Officials said in a news release that the federal on-site coordinator approved the joint plan on Thursday. Coast Guard Capt. Duke Walker had required the plan, and federal officials informed BP and Transocean they might be held responsible for the costs of identifying the source and the cleanup.

Federal scientists and BP say oil appears to have leaked last month from the drilling wreckage lying at the bottom of the Gulf of Mexico near where a BP well blew out in 2010, causing the nation's worst offshore spill.

A probe started after a sheen was discovered Sept. 16 in the waters near the site indicates the oil may have seeped from a mile-long metal tube, called the riser, which connected the Deepwater Horizon drilling rig to the Macondo well.

The plan calls for "satellite observations and mobilizing remotely operated vehicles to examine the original Macondo well area including the wreckage, debris and the riser on the sea floor," according to the news release.

The Coast Guard will oversee the remote vehicle mobilization Sunday, with operations taking place early next week, logistics and weather permitting.

The well itself, capped after more than 200 million gallons of oil spewed, is not believed to be leaking, officials said. The oil sheen posed no environmental threat because it was a small amount of oil and was far from land, federal officials said.

The announcement of oil leaking out comes at a sensitive time as BP and the Justice Department negotiate terms of a possible settlement to resolve government's claims against the oil giant. Several billion dollars are at stake if the talks produce a settlement for what likely will be record-setting civil and criminal penalties.