Image copyright AFP Image caption Twenty years after the first Rio summit, campaigners say this global gathering has failed to achieve similar results

On the final day of the UN sustainable development summit in Rio, UN chief Ban Ki-moon has urged governments to eliminate hunger from the world.

The secretary-general said in a world of plenty, no-one should go hungry.

The final phase of the summit has seen pledges from countries and companies on issues such as clean energy.

But a number of veteran politicians have joined environment groups in saying the summit declaration was "a failure of leadership".

And UK Deputy Prime Minister Nick Clegg described the outcome as "insipid".

The meeting, marking 20 years since the iconic Earth Summit in the same city and 40 since the very first global environment gathering in Stockholm, was aimed at stimulating moves towards the "green economy".

But the declaration that was concluded by government negotiators on Tuesday and that ministers have not sought to re-open, puts the green economy as just one possible pathway to sustainable development.

Mary Robinson, formerly both Irish president and UN High Commissioner for Human Rights, said it was not enough.

Despite the fact that the world produces enough food to feed everyone, there are more hungry people today than when the world last met in Rio in 1992 Barbara Stocking, Chief Executive, Oxfam

"This is a 'once in a generation' moment when the world needs vision, commitment and, above all, leadership," she said.

"Sadly, the current document is a failure of leadership."

The former Brazilian President Fernando Cardoso, who chaired the 1992 Earth Summit, said the declaration did not do as much for environmental protection as for human development.

"This old division between environment and development is not the way we are going to solve the problems that we are creating for our grandchildren and great-grandchildren," he said.

"We have to accept that the solutions to poverty and inequality lie in sustainable growth, not growth at all costs."

Mr Ban had hoped the summit would take firmer steps towards ensuring the poor had access to water, food and energy.

However, his flagship Sustainable Energy for All initiative was merely "noted" in the text, not enthusiastically endorsed.

'Ray of hope'

In the meeting's final phase, he challenged governments to do more.

Image copyright Reuters Image caption The summit was supposed to ensure access to water, food and energy for the world's poor

"In a world of plenty, no-one, not a single person, should go hungry," he said.

"I invite all of you to join me in working for a future without hunger," he told the estimated 130 heads of state and government in Rio.

Currently, it is estimated that almost one billion people - one seventh of the world's population - live in chronic hunger, while another billion do not receive adequate nutrition.

Measures that could help address this include eliminating food waste - about one-third of food is thrown away in rich countries and an even higher proportion in the poorest, for different reasons - and doubling the productivity of smallholdings.

The challenge is partly based on Brazil's own "hunger zero" programme, started by President Lula de Silva.

"Ban Ki-moon's announcement is a welcome ray of hope in a summit that has been shamefully devoid of progress," said Oxfam's chief executive Barbara Stocking.

"Despite the fact that the world produces enough food to feed everyone, there are more hungry people today than when the world last met in Rio in 1992," she said.

However, for the moment, a challenge is all it is.

There is no new money, and no changes to the way the UN organisation itself approaches the issue of hunger.

Outside the main negotiations in Rio, companies and governments have made well over 200 pledges of voluntary action in various areas.

Energy, water and food are all in that mix - though outnumbered by pledges to include sustainability issues in education programmes.