Negotiators at the UN climate talks late Saturday battled against time, exhaustion and division in the hope of salvaging a landmark deal on global warming.

More than a day after the scheduled end of the UN climate talks, the conference under the UN Framework Convention on Climate Change (UNFCCC) was heading for its 14th day -- and a second unbroken night of wrangling.

It is a record even by the fractious standards of climate politics: the talks were originally intended to run for just 12 days.

But the marathon was straining to the very limit the nerves among ministers or their stand-ins in the 194-nation forum.

"We can achieve a major breakthrough in the history of this convention," Brazil's top climate official, Luiz Alberto Figueiredo, said as he pleaded for the sometimes acerbic debate to be curtailed.

Veteran observers refused to bet on the outcome. They did not rule out an new bust-up, just two years after the stormy Copenhagen Summit.

But hopes at the conference centered on a political deal being crafted behind closed doors.

Pushed by the European Union (EU), the scheme would ensure the survival of the Kyoto Protocol, a landmark treaty defended by poor countries but increasingly dismissed by rich ones as out of date.

It would also, for the first time, lead to a legally binding agreement by 2015 which would bring all economies -- including the emerging giants and the United States -- under the same roof.

A loose coalition of nearly 90 African countries, least-developed nations and small island states, along with Brazil and South Africa, have rallied behind the EU "roadmap."

But so far Washington, Beijing and New Delhi have not shown their hands, though clues have leaked out of the negotiating sessions on their bottom lines.

One of the biggest stumbling blocks in the proposed compromise was just two words: the term "legally binding."

This terminology is perceived as political dynamite in Washington, given the powerful conservative currents in Congress -- and the presidential elections less than a year away.

India and the United States are also reluctant to see the new pact go into force before 2020, a delay that many vulnerable nations -- already suffering serious climate-related impacts -- will be reluctant to accept.

Plenary sessions Saturday focussed on the two tracks of a highly complex negotiating process, but ran into immediate problems.

Leftwing Latin American countries and poor nations in Africa complained fiercely about gaps in text or failures to address climate change more vigorously.

EU negotiators were not discouraged.

"I don't give up and I will never give up, until all possibilities are exhausted," European Climate Commissioner Connie Hedegaard told journalists.

"It would be such a pity if the world wasted this opportunity."

More and more ministers abandoned the conference to catch their planes home, yielding their authority to senior officials with less clout to broker a deal.

"Ministers have already started to leave," said Alden Meyer of a US thinktank, the Union of Concerned Scientists (UCS).

"I don't know when they lose critical mass on this front, in terms of ability to reach political compromises."

Memories in the UN climate process remain deeply scarred by the 2009 Copenhagen Summit.

Intended to set the seal on a historic treaty, that conference nearly collapsed amid nit-picking and finger-pointing. Face was saved in the final hours by a lowest-common-denominator deal cobbled together in back rooms.

One option in Durban, given the chaos of unfinished business, would be to suspend the meeting until the middle of next year, said some European delegates.

Research presented at Durban said that voluntary carbon pledges under the so-called Copenhagen Accord are falling far short of the goal of limiting warming to two degrees Celsius (3.6 degrees Fahrenheit).

In fact, the world is on track for a 3.5 C (6.3 F) rise, a likely recipe for droughts, floods, storms and rising sea levels that will threaten tens of millions, according to German data.