RIO DE JANEIRO — US energy giant Chevron said Monday it has suspended drilling following an oil spill in waters off Rio de Janeiro state which prompted Brazil to demand a "rigorous investigation."

Chevron Brazil said it was "responding to oil seeps and a subsequent sheen that has occurred in the vicinity of the Chevron-operated Frade project located 370 kilometers (230 miles) offshore northeast of Rio De Janeiro in water depths of approximately 1200 meters (3800 feet)."

"A precautionary suspension of development drilling activities at Frade remains in place," said the company, which estimated the volume of the sheen to be "between 400-650 barrels of oil."

Chevron said investigations were continuing to determine the cause and source of the oil seeps.

It added that 17 vessels were working on a rotational basis to deploy containment booms and undertake skimming and washing techniques aimed at controlling the sheen.

And it said inspections of the Frade facility "continues to confirm that production activities are unrelated to the seeps and sheen, and production is continuing."

Brazilian President Dilma Rousseff has demanded a "rigorous investigation into the causes of the accident."