COP21: 'Conditions never better' for climate change deal
Negotiators in Paris are again working through the night in an effort to secure a new global climate deal.
The French president of the meeting said the "conditions were never better" for a strong and ambitious agreement.
Laurent Fabius said he was confident of presenting the final draft early on Saturday morning.
The document will be assessed by participants before a final plenary meeting of all the parties to approve the deal.
Despite insisting throughout the conference that the deal would be done by Friday evening, Mr Fabius had to concede to the reality that critical issues remained and extra time would be needed.
Observers were concerned about the slippage, saying there were some concerns now that the time for compromises would run short.
"There has to be a take-it-or-leave-it text on Saturday," said Dr Diarmuid Torney from Dublin City University.
"With the length of time needed for processing and revising the document, whatever is released will be France's pitch for the final agreement," he told BBC News.
COP21 Live: Day 12 as it happened.
Significant progress had been reported on a range of issues in the latest version of the document, with evidence of real compromise between the parties.
Countries supported a temperature goal of 2C but agreed to make their best efforts to keep the warming rise to 1.5C. However, the language on cutting emissions in the long term was criticised for significantly watering down ambition.
Despite the advances, the talks seemed stuck on a number of important questions.
The question of demarcation between countries, called differentiation in the talks, was still the root cause of the difficulties.
"It's not an empty principle. It's an overarching provision or structure of whole agreement," said Gao Feng, China's special representative for climate change negotiations.
"So it's not just a one line or phrase in the preamble, or in one single article - but it will be reflected in different articles."
Another major difficulty was transparency. Richer countries want a single system of measuring, reporting and verifying the commitments countries make as part of this agreement.
It's said to be crucial to the US, which wants to ensure that China is subject to the same sort of oversight as it is. China and India are not keen on this type of oversight. It is proving a difficult nut to crack.
One positive note came with the announcement that Brazil was willing to join the so-called "high-ambition coalition" of countries including the EU, the US and 79 countries.
The alliance said it would push for an ambitious and legally binding deal with a strong review mechanism.
Global leaders also joined in efforts to move things forward.
US President Barack Obama spoke to his Chinese counterpart Xi Jinping by phone on Friday, with both leaders saying they were committed to an "ambitious" deal.
"Both leaders agreed that the Paris conference presents a crucial opportunity to galvanise global efforts to meet the climate change challenge," a White House statement said.
"They committed that their negotiating teams in Paris would continue to work closely together and with others to realise the vision of an ambitious climate agreement."
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UN climate conference 30 Nov - 11 Dec 2015
COP 21 - the 21st session of the Conference of the Parties - has seen more than 190 nations gather in Paris to discuss a possible new global agreement on climate change, aimed at reducing greenhouse gas emissions to avoid the threat of dangerous warming due to human activities.
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