Sha Zukang, secretary-general of the United Nations Conference on Sustainable Development, or Rio+20, asked countries to take tangible action as developed countries are thought to be backtracking from their previous commitments amid economic woes.

The three-day final meeting of the Preparatory Committee of the conference started on Wednesday in Rio De Janeiro, Brazil, to hammer out a draft action plan for leaders to discuss at the official conference next week.

"Today we begin the final stretch in the marathon of the negotiation process. Delegates will fine tune the text before the official conference starts," Sha said at a press conference on Wednesday.

The official conference will start next Wednesday with leaders from more than 130 countries and around 50,000 participants expected to attend.

Even though countries have showed a strong willingness to work together, the previous round of negotiations in New York was "challenging", Sha said.

The conference will likely result in a "focused" political outcome, concentrating on the big picture. The agreement won't be legally binding one, but a "political binding" agreement among members.

"This outcome, as has been repeatedly emphasized, should be action oriented… The whole world is watching us, and we cannot afford to let them down," he said.

To speed up negotiations, the talks were divided into two working groups dealing with different parts of the draft outcome text.

The most challenging issues are those defining a framework for action towards sustainable development, finance, capacity building and technology transfer, Sha said.

The Group of 77 plus China proposed to create a global fund for sustainable development with an initial $30 billion a year.

"This proposal has considerable backing and, therefore, it's part of the current negotiations," said Ambassador Luiz Alberto Figueiredo, Under Secretary at the Brazilian Foreign Ministry.

Developed countries are unwilling to abide by their previous commitments due to the financial crisis, said Figueiredo, adding that an agreement on means of implementation will be one of the "crucial issues" at the Rio meeting.

Twenty years ago, the Rio conference adopted the 1992 Rio Declaration on Environment and Development with about 27 principles.

Figueiredo said the result reached then was impressive, but now countries have to look back and see what's done and what's not.