UN climate talks spilled into an extra day Saturday as negotiators battled in Lima to end a standoff between rich and developing nations on the underpinnings of a world carbon-cutting pact.

A years-old dispute over sharing responsibility for curbing greenhouse gases reemerged to drive the 12-day negotiations into a familiar end-phase of poker-like holdout, clouding prospects for the ambitious environmental accord.

The talks had been scheduled to end at 6:00 pm (2300 GMT) Friday, but ran into the small hours as officials and ministers horse-traded over elements of a draft text.

At about 3:00 am on Saturday, the meeting secretariat announced an official postponement until 10:00 am of the closing session of a working group tasked with finalizing the document.

This must happen before the official adoption of agreements can take place in a broader plenary meeting.

Negotiators have to whittle the draft down to a consensus text to guide a process next year of declaring national pledges for curbing Earth-warming fossil fuel emissions.

"We are almost there. We need to make just a final effort," Peruvian Environment Minister Manuel Pulgar-Vidal pleaded with negotiators on Friday afternoon.

"We need to take political decisions."

Underlying the gridlock is the principle of "differentiation" -- a bugbear of the years-long attempt to bring all the world's nations into the fold of a single mechanism for braking planet-threatening climate change.

Developing nations insist the West must bear a bigger burden for carbon cuts, having started decades earlier to pollute their way to prosperity.

But rich countries point the finger at developing giants like China and India furiously burning coal to power their rapid growth.

Developing nations further demand that pledges incorporate not only action on reducing carbon emissions, but also financial help and adaptation aid to shore up their climate defenses.

Pledging rules must be finalized in the Peruvian capital to allow countries to start their submissions from the first quarter of next year.

These national contributions will be at the core of a global climate pact that nations have agreed to sign in Paris in December 2015, to enter into effect by 2020, seeking to limit average global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels.

- 'No progress' -

A new version of the draft document was distributed early Saturday, with the intention of holding a meeting straight away for it to be passed and then submitted to the plenary for adoption.

Pulgar conceded the text was "not perfect", but said it reflected common ground.

Parties insisted on time to reflect.

Campaigners in Lima feared the process would yield a weak-willed compromise, and pointed out that the latest draft placed no obligation on rich countries to spell out adaptation help or finance commitments in their pledges.

The latest draft merely "invites" all parties to "consider communicating their undertakings in adaptation planning or consider including an adaptation component."

Poor countries and small island states at risk of sea-level rise are also concerned that the draft mentions no mechanism to help them foot the bill for damage induced by climate change.

"The latest text released during the night was left completely bare. Climate finance, loss and damage and meaningful assessment of contributions have been removed," said Christian Aid climate advisor Mohamed Adow.

This meant that "almost no progress would be made at Lima and all the work punted down the road to be fought over next year in Paris."

The goal of concluding a global pact was set down in Durban in 2011, but negotiations on its scope and scale have been a minefield.

A major blocking point is whether or not there should be a process to assess the pledges' global impact on the 2 C goal -- with China a vocal opponent.

The new draft mentions a "non-intrusive and facilitative dialogue, respectful of national sovereignty".

Negotiators must also emerge from Lima with a broad outline for the pact itself, to be further developed in the months ahead.

Scientists say 2 C warming is relatively safe but no guarantee against damage to the climate system.

On current carbon trends, they say, the planet is on course for around 4 C warming this century, dooming future generations to a planet of worsening drought, flood, storm and rising seas.

The UN's Intergovernmental Panel on Climate Change says emissions must be slashed by 40-70 percent by 2050 from 2010 levels and to near zero or below by 2100 for any chance at 2 C.