UN climate talks have gone into overtime as rich and poor nations butted heads over who should be doing what to stave off dangerous planet warming.
Exhausted negotiators and ministers meeting in Warsaw geared for another late-night struggle to try to forge an ambitious climate pact, which must be signed in Paris by December 2015.
Nations remained deeply divided, delegates said.
They argued over apportioning carbon emissions curbs that will limit global warming to a safer 2.0 degrees Celsius, and over funding for climate-vulnerable poor countries.
"It is indeed one sleepless night in front of us but we are still hoping to close the meeting as soon as possible," said Polish Deputy Environment Minister Beata Jaczewska, whose country has hosted the 11-day parlay.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Gathering delegates from more than 190 nations, the annual negotiations are meant to lay the groundwork for a historic deal by the end of 2015 that will brake the climate juggernaut.
"If we don't succeed in Paris, the chances of us meeting the goal of limiting global warming to 2.0 degrees Celsius will be limited, or none," French Development Minister Pascal Canfin told negotiators.
With bureaucrats unlikely to reach agreement on the outstanding issues by Friday's scheduled close, "there's going to have to be a political package negotiated by ministers some time tonight or more likely tomorrow morning," said Alden Meyer of the US-based Union of Concerned Scientists.
A major sticking point was the demand by some developing nations like China and India, their growth fuelled by fossil fuel combustion, for guarantees of less onerous emissions curbs compared to wealthy nations.
In hotly disputed language, some want the new deal to impose "commitments" on the West and seek only "actions" from emerging economies.
The issue led to Europe and a group of developing economies trading barbs on Friday evening.
European climate commissioner Connie Hedegaard accused a group of "like-minded" countries of opposing a "push" towards the 2015 deal by insisting on the rich-poor country firewall.
"It is not acceptable to the European Union, but I also think to really many others," she told journalists.
A group calling itself the Like-Minded Developing Countries, which includes China and India as well as Pakistan, Malaysia, the Philippines, Saudi Arabia and Venezuela, took issue with what they called this "brazen attack".
"The EU chief is responsible for damaging seriously the atmosphere of confidence and trust in this process," said Venezuelan climate envoy Claudia Salerno, who claimed to speak on the group's behalf.
As emissions has been continuing to grow year after year, developing nations say their developed counterparts must have more responsibility for curbs given their long history of fossil-fuel combustion.
The West, though, insists emerging economies must do their fair share, considering that China is now the world's biggest emitter of CO2, with India in fourth place after the United States and Europe.
