UN climate talks fell into crisis on Saturday after some developing nations angrily rejected a plan worked out by US President Barack Obama and leaders of other major economies for fighting global warming.

Copenhagen, meant to be the climax of two years of negotiations, risked ending with no firm UN accords despite a summit of 120 world leaders on Friday who tried to work out the first climate blueprint since the UN's 1997 Kyoto Protocol.

Countries including Venezuela, Sudan and Tuvalu said they opposed a deal spearheaded on Friday in Copenhagen by the US, China, India, South Africa and Brazil at the summit. The deal would need unanimous backing to be adopted.

Opponents said the document, which sets a target of limiting global warming to a maximum 2 degree Celsius rise over pre-industrial times and holds out the prospect of $100 billion in annual aid from 2020 for developing nations, was too weak.

An acrimonious session long past midnight hit a low point when a Sudanese delegate said the plan in Africa would be like the Holocaust by causing more deadly floods, droughts, mudslides, sandstorms and rising seas.

The document 'is a solution based on the same very values, in our opinion, that channeled six million people in Europe into furnaces,' said Sudan's Lumumba Stanislaus Di-aping.

'The reference to the Holocaust is, in this context, absolutely despicable,' said Anders Turesson, chief negotiator of Sweden.

'This institution faces a moment of profound crisis at this meeting,' British Environment Minister Ed Miliband said. He urged delegates to accept the plan, which he said would improve the lives of millions.

UN blueprint

Other nations including European Union states, Japan, a representative of the African Union and the Alliance of Small Island States (AOSIS) urged delegates to adopt the plan as a UN blueprint for action to combat climate change.

'AOSIS stands by the document, we stand by the process,' said Dessima Williams, chair of AOSIS. 'It was not perfect, there were and still are things in it that we would not want.'

'We have a real danger of (UN climate) talks going the same way as WTO (trade) talks and other multilateral talks,' Maldives President Mohamed Nasheed said, urging delegates to back the plan to prevent the process dragging on for years.

For any deal to become a UN pact it would need to be adopted unanimously at the 193-nation talks.

If some nations are opposed, the deal would be adopted only as a less binding document or merely by its supporters -- a group representing far more than half the world's greenhouse gas emissions.

Many nations said the deal fell far short of UN ambitions for Copenhagen, meant as a turning point to push the world economy towards renewable energies such as hydro, solar and wind power and away from fossil fuels.

Before leaving, Obama said the deal was a starting point.

'This progress did not come easily and we know this progress alone is not enough,' he said after talks with China's Premier Wen Jiabao and leaders of India, South Africa and Brazil.

'We've come a long way but we have much further to go,' he said of the deal.

'The meeting has had a positive result, everyone should be happy,' said Xie Zhenhua, head of China's climate delegation.

European nations were lukewarm to a deal that cut out some goals mentioned previously in draft texts, such as a target of halving world greenhouse gas emissions by 2050.

'The decision has been very difficult for me. We have done one step, we have hoped for several more,' said German Chancellor Angela Merkel.

Australian Prime Minister Kevin Rudd called the deal 'a significant agreement on climate change action. It is the first global agreement on climate change action between rich nations and poor countries.'

Many European nations want Obama to offer deeper US cuts in greenhouse gas emissions by 2020.

But Obama was unable to, partly because carbon capping legislation is stalled in the US Senate. Washington backed a plan to raise $100 billion in aid for poor nations from 2020.

The deal sets an end-January 2010 deadline for all nations to submit plans for curbs on emissions to the United Nations. A separate text proposes an end-2010 deadline for reporting back on -- but dropped a plan to insist on a legally binding treaty.

Some environmental groups were also scathing.

'The city of Copenhagen is a crime scene tonight, with the guilty men and women fleeing to the airport,' said John Sauven, executive director of Greenpeace UK. – Reuters