Delegates at the World Summit in Johannesburg have heckled and interrupted US Secretary of State Colin Powell as he defended America's record on environmental issues.

Mr Powell, addressing the closing session of the summit, was jeered as he criticised Zimbabwe and talked of action the US was taking to meet environmental changes.

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 - have criticised America for obstructing a stronger final plan. They are also angry that President Bush has refused to attend the summit.

Jan Pronk, UN Secretary-General Kofi Annan's special envoy to the summit, 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".

World leaders are on Wednesday due to endorse the final action plan, which is intended to lift two billion people out of poverty and help protect the environment from the effects of development.

Mr Powell brought howls of protest when he said Zimbabwe had brought its population to the brink of starvation with its controversial land reform policies.

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."

Security guards removed at least two protesters from the chamber.

Colin Powell was drowned out by protests

South African Foreign Minister Nkosazana Dlamini-Zuma, who was chairing the conference, repeatedly called for order and said: "This is totally unacceptable."

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.

Negotiators earlier finalised a draft of the Plan of Implementation.

The final obstacle was resolved when a clause on access to health services had a reference to human rights and freedom added to one about cultural and religious values.

The move was aimed at stopping practices such as female circumcision or genital mutilation, which takes place largely in African countries.

The summit's 70-page action plan aims to help poor countries pursue economic development without doing undue harm to the environment.

Success questioned

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

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

Jan Pronk UN special envoy to summit

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

Environmental groups issued a statement on Wednesday saying the action plan failed to recognise the prime importance of human dignity.

They said it 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.

International aid agency Oxfam said the deal on the table offered only "crumbs for the poor".

It said the agreement was "a triumph for greed and self-interest, a tragedy for poor people and the environment".