A top official of British oil giant BP on Wednesday downplayed the U.S. government's claim that massive underwater oil plumes in "large concentrations" have been detected from Gulf of Mexico spill.

Oil from the Deepwater Horizon oil spill swirls in various colours in shallow water on East Grand Terre Island, Louisiana June 8, 2010. [Xinhua/Reuters Photo]

BP Chief Operating Officer Doug Suttles said on Wednesday's NBC news show that water tests confirmed subsea oil plumes from the spill, but insisted that concentrations are "very low."

"We haven't found any large concentrations of oil under the sea. To my knowledge, no one has," Suttles said.

Suttles' comments came one day after the National Oceanic and Atmospheric Administration said tests conducted at three sites by its researchers found subsurface oil as far as 142 miles from the leaking well.

It was the first government confirmation of undersea oil plumes near the blown-out well a mile beneath the ocean, since the explosion of BP-leased Deepwater Horizon drilling rig off the Louisiana coast on April 20.

"It may be down to how you define what a plume is here," said Suttles. "The oil that has been found is in very minute quantities."

Subsurface oil plumes are of concern because they can deplete the water's oxygen content and threaten marine life which is crucial to the ecosystem and fishing industry along the Gulf Coast.