An oil spill off Brazil's coast could be much bigger than earlier estimated, the Rio de Janeiro state environment minister said Friday, and Federal Police said that oil company Chevron drilled deeper than allowed.

Minister Carlos Minc didn't say how much oil has leaked from the site of a well owned by Chevron. The leak began Nov. 8 and some Brazilian officials say has not yet been contained.

The exact cause of the leak is not yet known, but a spokesman for Brazil's Federal Police, which has opened an investigation into the spill, said that Chevron "drilled about 500 metres farther than they were licensed to do."

The official spoke on condition of anonymity as he was not authorized to discuss the matter.

Minc is calling for more transparency on the part of Chevron.

"We can't trivialize this," he told the Globo TV network. "It's really serious and we don't yet know all the consequences. This incident has got to be much bigger than has been announced."

Satellite images to be released

The minister went on to say the government would soon release satellite images showing that the eight-kilometer oil slick is about one meter deep, rather than just on the surface, which Minc said would indicate that the environmental damage "is certainly bigger" than thought until now.

He added that marine life in the area of the spill, about 370 kilometres northeast of Rio de Janeiro in the Atlantic ocean, was sure to be affected, and that whales are migrating from north to south in that area at this time.

Chevron said the oil spill was between 400 and 650 barrels of oil, but that the company had contained the leak. The company said "current estimates place the volume of the oil sheen on the ocean surface to be less than 65 barrels."

The company has 18 ships working on a rotating basis to collect oil off the surface and monitor the slick.

The drilling contractor for the well is Transocean — the owner of the Deepwater Horizon rig that oil company BP was leasing at the time of last year's Gulf of Mexico oil spill, the largest in U.S. history.

Unclear if leak contained

Ana Carolina Oliveira, a spokeswoman for Brazil's oil regulator, the National Petroleum Agency, or ANP, has said an estimated 1,000 barrels had leaked to the surface and that it was still unclear if the leak was contained.

The nonprofit group SkyTruth, which uses satellite imagery to detect environmental destruction, said on its website the oil spill extended 2,379 square kilometres and that the spill rate as of Tuesday was up to at least 3,738 barrels per day.

Chevron said that cementing operations are taking place so that the well is plugged. ANP said in a note on its website that "the first stage of cementing, to permanently abandon the well, was successfully completed." The regulator says that the success of permanently plugging the well will be known "in the coming days."

ANP also said underwater footage showed that a "residual leakage flow" was continuing, but that "the oil slick continues moving away from the coast and is being dispersed, as desired."

Fabio Scliar, head of the Federal Police department's environmental affairs division, which is investigating the case, said those responsible would be held accountable.

"There is no doubt that a crime occurred. The spill comes from the drilling activity. What interests me now is to find who is responsible," Scliar was quoted by the Folha de S. Paulo newspaper as saying.

Calls to Scliar's office were not returned.