Ban said there was still a chance of limiting global warming to an internationally agreed ceiling of 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times to help avert floods, droughts, desertification and rising sea levels.

"But the window of opportunity is fast narrowing," he told delegates from about 190 nations at the Dec. 1-12 talks working on a deal, due in Paris in a year's time, to limit rising world greenhouse gas emissions.

"This is not a time for tinkering; it is a time for transformation," he said. Despite signs of progress, "I am deeply concerned that our collective action does not match our common responsibilities."

"We must act now," he said. He also urged wider involvement by the private sector.

The U.N. talks got a lift on Tuesday when the U.N.'s new Green Climate Fund reached a U.N. target of USD 10 billion for a first capitalization, helped by a pledge of about USD 166 million by Australia and USD 64 million by Belgium.

"We've got above one of the psychologically important milestones," Hela Cheikhrouhou, head of the fund, told Reuters. Pledges by 24 nations now total USD 10.14 billion, she said.

She said the fund, which aims to help developing nations cut emissions and adapt to changes such as heat waves and more powerful storms, was likely to start disbursing funds for projects in 2016.

Ban urged developed nations to "meet and exceed" a wider goal set in 2009 of mobilising at least $100 billion a year, in both public and private finance, by 2020 to help developing nations.

The Lima talks are trying to work out draft elements of a deal for Paris next year but face numerous fault lines about what should be included.

U.S. Secretary of State John Kerry is due to visit the talks on Thursday to add momentum.

Developing nations are pushing for a more ambitious outcome, with some calling for a target of cutting world greenhouse gas emissions to a net zero by 2050. OPEC nations, worried about loss of income from a shift to renewable energy, favour much vaguer long-term goals.

"We cannot have a climate agreement that condemns Mother Earth and humanity to death," in favour of enriching the few, Bolivia's left-wing President Evo Morales said, denouncing capitalism and consumption.

And Maria van der Hoeven, head of the International Energy Agency, said world leaders have a "golden opportunity" with plunging oil prices to put a price on carbon emissions since cheaper fuel makes the move less risky politically.

Separately, Peru's government denounced Greenpeace for laying out a banner promoting renewable energy near the famed Nazca lines, giant 1,500-year-old depictions of monkeys, hummingbirds and other creatures etched in the desert.

The government filed a criminal complaint against Greenpeace and asked a judge to ban activists who took part in the action from leaving the country.

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