Discord overshadowed debate about the world's environment at the Rio+20 UN summit Thursday, while celebrities clamored for a sanctuary to protect the riches of the Arctic.

On its penultimate day, UN chief Ban Ki-moon defended the first large-scale conference on sustainable development in a decade as "the beginning of a journey."

The event "will lead to a more sustainable future for ourselves and for generations to come," he said.

But the gathering -- which has drawn officials from around the world -- came under fire from the leftist presidents of Bolivia and Ecuador, along with indigenous peoples, who said capitalist greed lurked beneath its promotion of the green economy.

Bolivian President Evo Morales described the green economy as "a new colonialism" that rich nations sought to impose on developing countries.

"Countries of the north are getting rich through a predatory orgy and are forcing countries of the south to be their poor rangers," he said.

"They want to create intervention mechanisms to monitor and assess our national policies using environmental concerns as an excuse."

Morales, Bolivia's first indigenous president, also pressed African countries to protect their mineral wealth from transnational companies.

In an interview with AFP, President Rafael Correa of Ecuador accused rich countries of "looting the planet, consuming environmental assets freely."

Indigenous peoples gathered for a counter-summit issued a declaration describing the green economy as "a crime against humanity and the Earth" by dollarizing nature and stripping communities of their rights.

Greenpeace, meanwhile, announced that ex-Beatle Paul McCartney, actress Penelope Cruz and director Robert Redford had joined a campaign for a "global sanctuary" around the North Pole.

The celebrities are among the first 100 names on a planned million-signature scroll the activist group want to place on the seabed beneath Earth's northernmost point.

The goal is to counter nationalist claims on the North Pole and preserve the heart of the Arctic Ocean from a carve-up for resources.

The shrinkage of Arctic ice through global warming has led to jostling over sea routes and access to the sea bed, believed to be rich in hydrocarbons and minerals.

At Friday's close, the 190-nation summit is due to endorse a lengthy statement vowing to tackle Earth's environmental problems and entrenched poverty.

"This is a very good document, this is the vision on which we can build our dreams, our visions and it is important that the member states are united and work together," said Ban, who on Thursday also unveiled five objectives to put an end to world hunger.

But the Elders, a group of respected former leaders, environmental activists and poverty alleviation campaigners, slammed the draft as lacking ambition.

Mary Robinson, the former Irish president and ex-UN high commissioner for human rights, described it as "a failure of leadership" while former Norwegian premier Gro Harlem Brundtland said its "omission of reproductive rights is a step backwards."

"The failure of Rio+20 is a call for action which will give the people more energy to mobilize in the future," said Greenpeace political director Daniel Mittler, who called the summit an "epic failure."

Also Thursday, Ban unveiled five objectives of a "Zero Hunger Challenge" to ensure all the Earth's population "enjoys their right to food."

Separately Thursday, Paraguay's opposition-controlled Congress voted to start impeachment proceedings against President Fernando Lugo for his role in deadly clashes between police and squatters.

The brewing crisis prompted South American presidents at the conference to hold emergency talks and rush foreign ministers to Paraguay.