Battle lines have been exposed amid intense diplomatic wrangling as crucial United Nations climate talks reach their end game.
Ministers from more than 190 countries are gearing up to work through the night again at the summit in Paris to secure a final draft of the deal as the talks slip past their official Friday evening deadline.
French foreign minister Laurent Fabius, who is chairing the talks, said: "We are almost at the end of the road," as he outlined plans to publish the final draft on Saturday morning.
But key issues of finance for poor countries to deal with climate change, the different responsibilities of developed and developing countries to tackle climate change and pay for it, and the overall level of ambition in the agreement, are still the focus of political dispute.
A "high ambition coalition" of countries including the EU, some of the world's poorest and most vulnerable countries and the US, Chile, Colombia, Mexico, Iceland and Norway has called for a robust climate deal, with Brazil the most recent country to join the group.
Marshall Islands foreign minister Tony de Brum, the driving force behind the coalition, warned there had been a "co-ordinated campaign to gut the text" of ambition by some countries, and pledged to fight for a strong agreement.
Meanwhile US president Barack Obama has spoken on the phone to president Xi Jinping of China in the push to achieve an ambitious climate deal, the White House said.
The two leaders agreed the Paris conference was a crucial opportunity to galvanise global efforts to tackle climate change, and committed that their negotiating teams at the talks would continue to work closely together and with others to get an ambitious climate agreement, officials said.
As it stands, the agreement seeks to keep temperature rises to "well below" 2C above pre-industrial levels - beyond which dangerous climate change is expected - as well as to pursue efforts to limit the temperature increase to 1.5C, which vulnerable countries say is necessary to their very survival.
It would also see countries aiming to ensure climate change-causing emissions peak as soon as possible, and "undertake rapid reductions thereafter towards reaching greenhouse gas emissions neutrality in the second half of the century".
And it sets out a five-year cycle for reviewing and potentially raising the level of pledges countries have made to tackle climate change, which up to 2030 are currently not enough to put the world on a path to meet the 2C target, let alone the tougher 1.5C goal.
Rich nations would scale up public and private finance after 2020 from their pledged 100 billion US dollars (£60 billion) a year, to support developing countries in coping with the impacts of climate change and to develop cleanly, under the draft deal.
But the issue of "loss and damage" - the recognition that some of the most vulnerable countries need support to cope with irreversible impacts such as inundation of their land from rising sea levels - is still hugely difficult, with developed countries refusing anything that could open them up to liability or compensation.
One of the key sticking points in achieving a deal is the issue of "differentiation" - the difference in responsibilities for rich and poor countries to address the climate problem and pay for it.
Countries such as China and India want to maintain the clear distinction between developed and developing countries, set down in 1992 in the UN climate convention under which the talks are held, arguing rich nations are responsible for historical emissions and should be required to do most to tackle the problem.
Indian environment minister Prakash Javadekar accused developed countries of not showing flexibility towards poorer countries, and warned that unless rich nations showed the "spirit of accommodation", the success of the talks was not guaranteed.
But developed countries say that while they should take the lead on action and payments to help poor nations deal with climate change, all countries should take action to curb emissions - according to what they can do - because everybody has to act for the problem to be solved.
Despite the overrun and the thorny issues that need to be tackled, eminent economist Lord Stern - who wrote the key review on the economics of climate change - said it was the best atmosphere between countries that he had seen in 10 years of attending UN climate talks.
He put the change down to the fact that countries were now "seeing a way forward" that could tackle climate change and help address other issues such as giving people access to electricity and boosting economic growth.