The final day of the World Summit in Johannesburg has been marked by anger and disappointment at compromises on the key issues of tackling poverty and protecting the environment.

Delegates jeered and heckled US Secretary of State Colin Powell as he defended America's record on the environment and accused the Zimbabwe Government of pushing millions towards starvation.

Main points agreed

To halve the number of people in Africa lacking basic sanitation by 2015 To "substantially increase" renewable energy although no targets have been set To "significantly reduce" the loss of species by 2015 Increasing links between trade, environment and development Kyoto treaty on global warming revived by Russian backing

Environmental groups - who earlier staged a walk-out at the summit - criticised America for obstructing a stronger final plan. They were also angered by President Bush's absence from the summit.

The UN Secretary-General, Kofi Annan, admitted that the 10-day conference had not achieved all that had been hoped for it.

But he argued that "Johannesburg is not the end of everything, it is a beginning".

The summit ended by endorsing a final action plan aimed at tackling global problems ranging from Aids to depleted fish stocks - but with some delegations, including the United States, registering reservations about items in the document.

Disappointment

Mr Annan's special envoy to the summit, Jan Pronk, told BBC News Online that "there is a huge gap between what the delegates have managed to achieve here and people's expectations of them".

Colin Powell was drowned out by protests

Anger at the US boiled over when Mr Powell attacked the Zimbabwe Government's controversial land reform policies, inspiring howls of protest from some delegates.

As the summit chairman struggled to regain control, Mr Powell told the protesters: "I have heard you, now will you hear me?"

Mr Powell then criticised Zambia - also facing a food crisis - for rejecting genetically modified corn that Americans eat every day.

He said: "In the face of famine, several governments in southern Africa have prevented critical US food assistance from being distributed by rejecting biotech corn which has been eaten safely around the world since 1995."

Protesters removed

Demonstrators shouted "shame on Bush" and some unfurled a banner reading: "Betrayed by governments."

We need to look again at the whole system - officials got too bogged down in details

Jan Pronk UN special envoy to summit

Security guards removed at least two protesters from the chamber.

To more jeers, Mr Powell added: "We are committed not just to rhetoric and to various goals, we are committed to a $1bn programme to develop and deploy advanced technologies to mitigate greenhouse-gas emissions."

The US has been strongly criticised for its rejection of the Kyoto treaty on global warming.

Plan criticised

Mr Pronk, a former Dutch environment minister, said the summit had come "close to collapse".

Demonstrations also took place outside the conference

"They were working till last night on reinforcing advances made in the past. That left very little time for talking about implementation," he said.

Environmental groups issued a statement on Wednesday saying the action plan strengthened "an international economic and financial system that is incompatible with the goals of sustainable development" and failed to protect the Earth.

They have welcomed new targets on sanitation in developing countries and a promise to restore global fish stocks.

But there is disappointment at the failure to set a target for increasing the use of renewable energy. The move was blocked by the United States and oil producing countries.

As the summit ended, leaders also adopted a political declaration on sustainable development, pledging to create "humane, equitable and caring global society".