Ministers of more than 100 participating countries failed at preparatory talks in Bali, Indonesia, earlier this month to agree a draft action plan for the world's most important environmental summit, with rich and poor nations divided about the best ways to promote sustainable growth and development.

The conference in Johannesburg is being billed as the biggest-ever U.N. gathering. More than 100 heads of state and 60,000 delegates are expected to attend the summit and a parallel meeting of non-governmental organisations.

But environmental groups and non-governmental organisations have warned governments that the summit is heading for failure.

Mbeki, who will chair the Johannesburg summit, said the Bali meeting made progress on some issues, but left key decisions unanswered.

"The failure to find consensus in Bali on some of these issues places increased responsibility on the president, as chairperson of the WSSD, to ensure that a basis for agreement is developed between now and August.

"We will be starting a process of consultation with the major groupings in the United Nations system to explore the possibilities of finding consensus," said Mbeki, who usually refers to himself in speeches as "we".

Officials in Bali said the meeting failed to reach agreement on "essential" areas in the action plan such as timebound commitments and ways of financing pledges in the draft.

Mbeki said key issues still outstanding included ways to link the decisions of the Monetary Financing for Development Conference earlier this year with the goals of the Earth Summit and mechanisms to differentiate the responsibilities of different nations towards shared goals.

Mbeki pushed that conference into extra time, intervening personally to hammer out a partial accord which led many international critics to call the summit a failure.

Environmental groups have pinned much of the blame for the failure of the Bali conference on the U.S., accusing it of being reluctant to commit to some targets for action at home in the interests of business profits, charges members of the U.S. delegation here have denied.

The Johannesburg summit opens on August 26 and falls a decade after the landmark Earth Summit in Rio de Janeiro, which put environmental issues on the global political agenda.