Negotiations on a UN blueprint to fix Earth's damaged environment, eradicate poverty and promote green jobs hit snags on Monday two days ahead of a global summit.

Brazil wants to seal a deal swiftly to ensure that a three-day gathering, aimed at reviving the momentum of the 1992 Earth Summit, is not wrecked by squabbles.

But delegates attending the UN Conference on Sustainable Development in Rio said the 50-page draft was mired in discord.

Disputed issues include text on climate-altering fossil fuels, promoting the green economy and providing funding for poorer countries.

Another is how to strengthen world governance for the environment, an area where national sovereignty is jealously guarded.

A further problem area is "Sustainable Development Goals" -- SDGs -- that would replace the UN's Millennium Development Goals after these objectives expire in 2015.

"The conditions for an agreement are not there," said French Ecology and Sustainable Development Minister Nicole Bricq.

"What has been put on the table is not suitable for us," she said in an interview with AFP. "The proposed text lacks vision and ambition and there is no outlet for concrete actions."

She warned: "We can continue negotiating on until (Friday, the) 22nd."

German Environment Minister Peter Altmaier said the talks were "moving in the right direction, but it is just the beginning of the final, not yet critical, stage of the negotiations."

"We still believe that there is a considerable margin for improvement and we want to use every hour and every minute we have over the next couple of days... to see what we can do to make the conclusions clearer, sharper and more ambitious."

Around 100 heads of state and government are expected to attend the summit starting Wednesday, although several big hitters -- US President Barack Obama, British Prime Minister David Cameron and German Chancellor Angela Merkel among them -- will be absent.

The meeting is designed to crown a 10-day event, bringing together some 50,000 activists, policymakers and business executives to showcase sustainable development.

Twenty years have elapsed since the first Earth Summit, where the community of nations declared war on poverty and environment ills. They set up three conventions to tackle climate change, desertification and species loss and drew up a bible, Agenda 21, intended to guide their actions.

But on almost every count, the planet is sicker than before.

Scientists warn that emissions of climate-altering fossil-fuel gases are scaling ever-higher peaks, a trend that will stoke worse floods, droughts and storms and imperil small island states with rising seas.

Biodiversity loss, too, is unprecedented in the context of human history, and some biologists fear that a mass extinction is already underway.

The number of people living on $1.25 (one euro) a day fell from 1.9 billion in 1990 to around 1.3 billion in 2008. But in developing countries, nearly one person in two still lives on less than $2 (1.6 euros) per day.

Activists said they were worried that the final document would be gutted of ambition.

"Today I am very concerned and worried because the draft final document of the Rio+20 conference does not give proper attention to climate change," former Soviet president Mikhail Gorbachev said through an organization he has set up, the Climate Change Task Force, to combat global warming.

"It looks like there is backsliding on this issue and that is what worries me so much, because without addressing climate change, all of the other problems and tasks that will be set by the final document will not be accomplished and will become meaningless."

Jim Leape, director general of WWF International, urged Brazilian President Dilma Rousseff to intervene directly.

"The current negotiating text may be called 'the future we need', but it certainly doesn't have the commitments we need. There is still time for leaders to step up, and we need Dilma to lead the way."