Rich and poor countries squared off at climate talks in Warsaw on Wednesday as UN chief Ban Ki-moon called for "much bolder" action to stave off an existential peril.

The two sides squabbled over funds to help poor nations deal with global warming and apportioning curbs in greenhouse gases.

Amid the haggling, Ban urged parties not to lose sight of the big picture.

"Climate change is the greatest single threat to peace, prosperity and sustainable development," the UN secretary general told negotiators in the Polish capital.

Dozens of ministers joined a special meeting on finance as, in other rooms, work continued laboriously on a global pact that must be sealed by the end of 2015.

The deal must roll back emissions from fossil fuels to avert climate damage for future generations and help poor countries exposed to worsening storms, floods, droughts and rising seas.

With only two days left in this annual round, some observers and delegates said the talks were badly deadlocked, particularly on finance.

Developing nations are challenging wealthy countries to honour a 2009 pledge to muster up to $100 billion (74 billion euros) by 2020.

Still struggling with an economic crisis, the developed world is wary of unveiling a point-by-point plan at this stage, or pledging any new short-term figures.

"The 100 billion is a goal we need to establish a very clear roadmap for," insisted Indian Environment Minister Jayanthi Natarajan.

"Unless that is provided for, it will be impossible for us to take forward any meaningful discussion and we feel the negotiations will be rendered completely meaningless," she told journalists.

Tanzanian President Jakaya Kikwete said poor nations were doing their best to mobilise funds for climate change, but the costs were "just too high".

Funding hit by crisis

Poland's Marcin Korolec, chairing this year's negotiations, said the finance discussion was "challenging" and underscored the constraints caused by the economic crisis.

"We could not have predicted the economic darkness that we have all lived through for the past five years."

Ban said that to achieve the UN goal of limiting average global warming to 2.0 degrees Celsius (3.6 Fahrenheit) from pre-Industrial Revolution levels, "our target for scaling up climate finance must be much bolder."

The United States and Europe were quick to point to their own efforts.

US negotiator Todd Stern said his country had contributed about $2.7 billion in public money in 2013, "the highest number that we have had in the last four years". European Union envoy Connie Hedegaard said the 28-nation bloc had earmarked some 1.7 billion euros in 2014-2015.

The money crunch also lies at the heart of another issue bedevilling the talks: demands by developing countries for a mechanism to help them deal with climate-related losses and damage.

Rich nations fear being locked into never-ending liability for compensation.

Countries including the United States and Australia said there was no need to create a "loss and damage" mechanism separate from existing systems for dealing with climate change mitigation and adaptation.

Another bone of contention is deciding how to share out future emissions curbs.

Developing countries, many like China and India burning vast reserves of atmosphere-polluting coal to fuel their economic development, want wealthy nations to make deeper cuts to make up for their long history of emissions.

"Developed countries need to do more... now, and not transfer all the burden of climate change to the poor of the world after 2020," said India's Natarajan.

But US negotiator Stern dismissed this.

Any agreement in which "the developed countries would be treated in one way, in one section of the agreement, and developing countries in a different part of the agreement" was a "non-starter", he said.