UN Secretary-General Ban Ki- moon on Thursday expressed frustration at the slow pace of negotiations over a draft outcome document for the upcoming UN Conference on Sustainable Development (Rio+20), urging member states to look at the "bigger picture" of a sustainable future.

Rio de Janeiro will host an?UN Conference on Sustainable Development (Rio+20) from June 20 to 22, 2012. [un.org]

Less than one month before the landmark summit in Rio de Janeiro, Brazil, member states are still engaged in intense negotiations over the text of the document.

Lack of progress has prompted the states to agree to extend talks until June 2. If there is still no agreement, they will have their last chance in a final round of negotiations during the Rio summit, which runs from June 20 to 22.

"The negotiation has been painfully slow," Ban told reporters in a briefing at the United Nations Foundation office in New York.

"My message is that -- this is not the time to argue against small, small items," the secretary-general pleaded. "Please do not lose the bigger picture."

The Rio+20 is not the end, but the beginning of many processes, he said, calling on member states to be "flexible" and rise above national or group interests.

The UN chief voiced a guarded optimism toward the outcome of the conference. Despite some people's skepticism about a successful Rio conference, he said, "basically I am optimistic of the outcome of this meeting."

Ban recognized member states' hard work in boiling down an initial 6,000-page draft into the current 80 pages. "But still 80- page is too long. My message was that: please try to have a good outcome, a concise one, ambitious but practical and implementable. "

The secretary-general offered his wish for "three clusters of outcomes that will mark Rio+20 as a watershed." First, the event should inspire new economic thinking at a time when the old economy model is breaking down; second, Rio+20 should be a "people 's summit" which urges countries to put people's interest first while achieving economic growth; third, Rio+20 should issue a call for action to use the planet's resources like oceans, water, air and forest in a smarter way.

"Our planet has been very kind to us. Let humanity reciprocate by respecting our planet Earth," the secretary-general said.