Brazil plans to sink a decommissioned aircraft carrier that has been towed around the Atlantic for months with a damaged hull, drawing criticism from environmentalists, who say it is packed with toxic materials.

The navy and defense ministry said in a statement Wednesday that the six-decade-old warship, the Sao Paulo, would be scuttled, after trying in vain to find a port willing to welcome it.

"Given the situation and the growing risk of towing (the ship), in light of the deteriorating buoyancy of the hull and the inevitability of a spontaneous, uncontrolled sinking, there is no option but to jettison it in a planned, controlled sinking," it said.

Environmentalists attacked the decision, saying the aircraft carrier contains tonnes of asbestos, heavy metals and other toxic materials that could leach into the water and pollute the marine food chain.

The director of the Basel Action Network (BAN), Jim Puckett, accused Brazil's navy of "gross negligence."

"If they proceed with dumping the very toxic vessel into the wilderness of the Atlantic Ocean, they will violate the terms of three international environmental treaties," he said in a statement.

He urged President Luiz Inacio Lula da Silva -- who took office last month vowing to reverse surging environmental destruction under far-right ex-president Jair Bolsonaro -- to immediately halt the "dangerous" plan.

French environmental group Robin des Bois meanwhile called the ship a "30,000-tonne toxic package."

Built in the late 1950s in France, whose navy sailed it for 37 years as the Foch, the aircraft carrier earned a place in 20th-century naval history.

It took part in France's first nuclear tests in the Pacific in the 1960s, and deployments in Africa, the Middle East and the former Yugoslavia from the 1970s to 1990s.

Brazil bought the 266-meter (873-foot) aircraft carrier for $12 million in 2000.

A fire broke out on board in 2005, accelerating the aging ship's decline.

Last year, Brazil authorized Turkish firm Sok Denizcilik to dismantle the Sao Paulo for scrap metal.

But in August, just as a tugboat was about to tow it into the Mediterranean Sea, Turkish environmental authorities blocked the plan.

Brazil then brought the aircraft carrier back, but did not allow it into port, citing the "high risk" to the environment.

The navy said it had towed the ship to a location 350 kilometers (215 miles) off the Brazilian coast, with 5,000-meter-deep water, calling it the "safest area" for the operation.

It did not say when it planned to scuttle it.