Delegates have been poring over several draft texts on Friday
World leaders are locked in talks as they attempt to deliver a last-minute deal at the Copenhagen climate summit.
Confusion has dominated the final scheduled day as several draft texts were circulated on Friday afternoon.
The US, EU and China have not offered anything new in public, prompting fears that a meaningful deal to curb global emissions was slipping beyond reach.
US President Barack Obama held a second meeting with China's premier in an effort to break the deadlock.
The talks are now expected to continue late into the night.
COPENHAGEN DRAFT TEXT
"Recognises the scientific view" on keeping temperature rise below 2C (3.6F) but does not set it as a target
No date for peaking emissions - just "as soon as possible"
Developing countries to monitor and verify their own emissions without international oversight
"Support a goal" of raising $100bn per year by 2020, not commit to achieving that goal
No date for concluding a detailed agreement, nor whether it should be legally binding
Delegates are currently considering a fourth draft, which is being called the "Copenhagen Accord".
It calls for global emissions to be cut by 50% from 1990 levels by 2050, with "Annex I Parties" (industrialised nations except the US) committing to cuts of 80% by the same time.
Other nations would "implement mitigation actions", in the form of national action plans, that would be updated every two years.
The text also acknowledges the scientific view that nations need to keep emissions below a level that stops the global average temperature exceeding a 2C (3.8F) increase above pre-industrialised levels.
This is the temperature that scientists believe could trigger dangerous climate change.
However, in an apparent concession to developing nations, the document calls for this stance to be reviewed by 2016.
"This review would include consideration of strengthening the long-term goal to limit the increase... to 1.5 degrees (2.7F)," it states.
This is the threshold that a number of nations vulnerable to rising sea levels, such as small island nations, have been calling for during the two-week talks.
On the potential finance package to help developing nations cope with the impact of climate change, the text says: "Developed nations support a goal of mobilising jointly $100bn a year by 2020."
'Time to act'
Earlier, versions of the draft political agreement drawn up by a small group of countries were rejected during overnight discussions.
US-LED COPENHAGEN DEAL
No reference to legally binding agreement
Recognises the need to limit global temperatures rising no more than 2C above pre-industrial levels
Developed countries to "set a goal of mobilising jointly $100bn a year by 2020 to address the needs of developing
countries"
On transparency: Emerging nations monitor own efforts and report to UN every two years. Some international checks
No detailed framework on carbon markets - "various approaches" will be pursued
The EU did not raise its offer on cutting emissions from 20% to 30%, as some commentators had anticipated.
The bloc decided last year that it would adopt the higher target if there was a comprehensive global agreement on climate change here.
Many observers had expected - and hoped - that the EU would raise its targets for cutting emissions from 20% to 30% by 2020 (from 1990 levels).
BBC environment correspondent Richard Black said this was a clear indication that things were not proceeding towards the kind of deal that the EU had wanted.
Addressing the summit on Friday, President Obama said: "While the science of climate change is not in doubt, I think our ability to take collective action is in doubt right now, and it hangs in the balance."
China's 'special difficulty' on climate
China's Premier Wen Jiabao told delegates: "To meet the climate change challenge, the international community must strengthen confidence, build consensus, make vigorous efforts and enhance co-operation."
He added that in addressing climate change, the international community must not "turn a blind eye to historical responsibilities, per capita emissions and different levels of development".
Correspondents say it is the US and China - the world's two largest carbon emitters - that hold the key to striking an agreement. China has been criticised during the summit for not offering stronger carbon emissions targets and for resisting international monitoring of its emissions controls.
The US has received criticism for making its climate aid offer so late in the talks.
COPENHAGEN CLIMATE SUMMIT
Delegates from 193 nations are in Copenhagen to negotiate an agreement on curbing greenhouse gas emissions, in order to prevent dangerous climate change
Developing nations want rich nations to cut emissions by at least 25% by 2020 - rich nations are reluctant to go so far
The US insists China curbs its emissions, and allows international verification
Poor nations want climate aid to come largely from public finances, while the West favours schemes like carbon trading
On Thursday, US Secretary of State Hillary Clinton said the US was prepared to help establish funding of $100bn a year for developing countries if a deal emerged that met US requirements.
The key US demand is "transparency" from China, seen as a must if the US Senate is to pass legislation controlling emissions.
Brazil's President Luiz Inacio Lula da Silva received rousing applause for his speech. He told delegates: "We, the developing countries... when we think in money, we should not think that someone is paying us a favour.
"We should not think that someone is giving something that we are begging for, because the money that would be put on the table is the payment for greenhouse emissions released over two centuries by those countries that industrialised themselves first."
President Lula added: "I would love to leave Copenhagen with the most perfect document in the world... I'm not sure if some angel or wise man will come down to this plenary and put in our minds the intelligence that we lacked up until now. I don't know if that's going to be possible."
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