Brazil sank a decommissioned aircraft carrier in the Atlantic Ocean off its northeast coast, the Brazilian Navy said, despite warnings from environmentalists that the rusting 1960s French-built ship would pollute the sea and the marine food chain.

The 32,000-tonne carrier had been floating offshore for three months since Turkey refused it entry to be scrapped there because it was an environmental hazard and the ship was towed back to Brazil.

The carrier was scuttled in a "planned and controlled sinking" late on Friday, the Navy said in a statement, that would "avoid logistical, operational, environmental and economic losses to the Brazilian state," it said.

The hull of the Sao Paulo was sunk in Brazilian jurisdictional waters 350 kilometers (217 miles) off the coast where the sea is 5,000 meters deep, a location chosen to mitigate the impact on fishing and ecosystems, the Navy said.

Federal public prosecutors and Greenpeace had asked the Brazilian government to stop the sinking, saying it was "toxic" due to dangerous materials, including 9 tonnes of asbestos used in paneling.

"The sinking of the aircraft carrier Sao Paulo throws tons of asbestos, mercury, lead and other highly toxic substances into the seabed," Greenpeace said in a statement. It accused Brazil's Navy of neglecting the protection of the oceans.

The Clemenceau-class aircraft carrier served the French Navy for four decades as the Foch, capable of carrying 40 war planes.

Defense expert and former foreign policy congressional staffer Pepe Rezende said the carrier was bought by the Brazilian Navy for just $12 million in 1998 but needed an $80 million refit that was never done.

After the carrier was decommissioned, Turkish marine recycling company Sök Denizcilik Tic Sti bought the hull for $10.5 million, but had to tow it back across the Atlantic when Turkey barred entry to its shipyard.

Brazil's Navy said it asked the company to repair the carrier at a Brazilian shipyard, but after an inspection showed it to be taking on water and was at risk of sinking, the Navy banned the ship from entering Brazilian ports. It then decided to sink the Sao Paulo at high sea.

The company's legal representative in Brazil, Zilan Costa e Silva, said that disposal of the carrier was the Brazilian state's responsibility under the 1989 Basel Convention on the transboundary movement of hazardous wastes.

Greenpeace said the sinking violated the Basel Convention, the London Convention on the prevention of marine pollution, and the Stockholm Convention on persistent organic pollutants.

"The Brazilian Navy chose to harm the environment and lose millions of dollars rather than allow public inspection of the ship," Greenpeace said, calling the sinking the "biggest breach of chemical and waste agreements ever committed by a country."