The head of the US delegation at UN climate talks has warned of a "major breakdown" in the process if negotiators fail to come to an agreement at a meeting in Lima, Peru.
Talks remain deadlocked by divisions between rich and poor countries over the scale and scope of plans to tackle global warming.
The talks were due to have concluded on Friday but have now overrun.
Disagreements abound over a key building block of a new global treaty.
That element, known as Intended Nationally Determined Contributions (INDCs) in the jargon of the meeting, is seen as a major step as developed nations are due to make pledges on how they will tackle climate change by the end of March next year.
The countries came to Peru to work out the details of what those pledges would entail.
It has not been smooth sailing.
The big emitters like the US and EU want these pledges to be focused mainly on cutting carbon - and they want to include emerging economies such as India and China.
Developing countries object strongly to any attempts to bring them into the fold - and they argue that the pledges of the rich must include substantial finance for the poor.
According to US climate envoy Todd Stern, the deadlock on this and other issues threatens the chances of a new global deal next year.
"Failing to produce the decision before us will be seen as a major breakdown, and will deal a serious blow to the confidence of the parties and others as we approach Paris. And indeed to the hope of a Paris agreement," he said.
The president of the meeting, Manuel Pulgar-Vidal, has attempted to move things forward by producing a new draft text.
Developing countries were not impressed. They argued that the new text went too far in watering down a key element of the climate convention signed in 1992, the idea of common but differentiated responsibility (CBDR).
This in effect divided the world between richer countries who have had to take on carbon cutting burdens and poorer countries who have no obligations.
Lima climate talks
- Conference scheduled to run from 1 to 12 December, attended by 195 countries
- Negotiations aim to advance the outline text of an agreement on climate change, to be finalised in Paris by the end of 2015
- Progress on approving the text has been slow
- Countries are divided over whether developing countries should take on obligations to cut emissions
- The talks come amid some of the hottest global average temperatures ever on record
The developed say the world is very different now than in 1992, with more than half the world's emissions coming from the emerging economies. But many of the delegates here rejected the idea of change.
"Many of you colonised us so we started from very different points… this you must appreciate," said a delegate from Malaysia, who was strongly arguing for a retention.
"There is a world out there which is different to your world," he warned the parties.
Some of the negotiators believed that the president had gone too far in cutting out some of the elements that they felt were crucial to those most affected by climate change. They argued that language on finance and loss and damage had been weakened or removed.
"If you are submitting yourself for circumcision", warned Singapore's Environment Minister, Vivian Balakrishnan, "be very sure it doesn't become an amputation."
Many felt that a group of countries called the Like-Minded Developing Countries (LMDC) - which includes China, India, Saudi Arabia and Venezuela - were the key hold outs against a compromise.
"Three-quarters of the people in there are happy with the deal," said one delegate, gesturing to the hall where countries are gathered. "It's the like-minded group who are holding it up."
The president of the meeting has held a series of 10-minute meetings with all the parties and it is expected that a new or amended text will soon be presented for a final decision.
The worry is that to secure wide support, the document will be significantly weakened, with negative implications for a treaty in Paris.
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