US energy giant Chevron said Tuesday it would seal and abandon an errant oil well which for the past week has seeped oil into waters off Brazil's Rio de Janeiro state.

The well, which is leaking crude at the rate of some 400 barrels per day, is located about 1,200 meters (4,000 feet) underwater.

Chevron Brazil said it devised a plan, approved by Brazil's National Petroleum Agency, to encase the well in cement, ensuring that it will never be accessed again. The well has been leaking since last Tuesday, the company said.

The company said on Monday that the mishap at its Frade project some 370 kilometers (230 miles) northeast of Rio De Janeiro has created a widening oil slick, prompting the cessation of drilling activities.

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

Brazil's President Dilma Rousseff has demanded a "rigorous investigation into the causes of the accident."