Image caption Campaigners are calling for a strong global climate deal that is legally binding

The EU and some of the world's poorest nations have launched a joint bid for a strong outcome at the UN climate talks.

Ministers from rich and poor countries stood shoulder to shoulder at a news conference urging big emitters such as China and the US to move to a deal.

The US said it backed the EU plan for a "roadmap" to a binding outcome, though small island states' ministers said it had not shown support in negotiations.

Talks deep into Thursday night failed to reconcile countries' differences.

But the mood was reportedly constructive, and observers say the outcome of the talks is still too close to call.

The alliance between the EU, the Alliance of Small Island States (Aosis) and Least Developed Countries (LDCs), brokered by Denmark and Gambia, covers more than half the world's governments.

Some other countries in Africa and Latin America also support its aims.

The very public show of co-operation between developed and developing countries is possibly unprecedented in the UN climate convention's history, and marks a new dynamic in the often fractured process.

"We're very happy to have with us the EU and the Least Developed Countries in an effort to inject new momentum into the negotiations," said Danish climate minister Martin Lidegaard.

"Our united goal is that we live up to a maximum 2C increase in temperature, if possible 1.5C, and we all know that we need to act now if that's to be possible."

His Gambian counterpart, forestry and environment minister Jato Sillah, said that for the LDCs, keeping the global temperature rise down was a matter of survival.

"We thank the EU for taking a common ground initiative for all countries to come on board and ensure that we have a decision from Durban.

"We must have a decision - we must show the world that we are willing to take our role and our responsibilities [seriously]."

Later, the new grouping issued a joint statement saying that "What we need is not more thinking. What we need is more action".

Head for success

The alliance is looking for three key things: continuation of the Kyoto Protocol in meaningful form, fulfilment of pledges on finance, and an agreed mandate to negotiate a new legally-binding agreement as soon as possible that will constrain emissions by all the big players.

Image caption Protesters accuse US politicians of obstructing progress towards a legally binding agreement

The US and a number of big developing countries including Brazil, China and India want any negotiations to start in 2015 at the earliest, and not come into effect until after 2020.

For Aosis and the LDCs, that is too late, as it will almost certainly mean global temperatures increasing by more than 1.5C and potentially damaging consequences such as drought and sea-level rise.

Brazil's environment Minister Izabella Teixiera told BBC News that decisions on further emission cuts should be made after the next Intergovernmental Panel on Climate Change report in 2013/14.

But she left open the possibility of movement.

"Everybody wants success, everybody wants to work together... so we are flexible," she said.

Earlier, in a news conference, US envoy Todd Stern had surprised observers by backing the EU notion of a "roadmap".

Climate change glossary Select a term to learn more: Adaptation Adaptation Action that helps cope with the effects of climate change - for example construction of barriers to protect against rising sea levels, or conversion to crops capable of surviving high temperatures and drought.

Looking somewhat ashen-faced after what has doubtless been a gruelling fortnight, Mr Stern said there was a "misconception" that the US wanted to delay action on climate change until after 2020.

"We are strongly committed to a promptly starting process to move forward," he said.

But precisely what timetable Mr Stern had in mind was not clear.

And Aosis representatives seemed to be surprised by the news of US support for an early beginning.

"I would say 'thank you very much'," said Karl Hood, Grenada's foreign minister.

"I would say 'let me see that in the negotiating room, let me see that in the text, let me see that while we sit around the table putting the text together'."

The US State Department later issued a clarifying notice, saying Mr Stern had said the US "could support a process to negotiate a new climate accord - he did not say the US supports a legally binding agreement as the result of that process".

Midnight oil

Ministers and their negotiators officially have until the end of Friday to reach a deal, although everyone expects the talks to last through the night into Saturday.

There is some concern that the South African hosts have not shown the urgency or the organisation needed to bring such a complex set of negotiations to a conclusion.

One delegate went as far as to describe the organisation as "shambolic", though others were more restrained.

With the official documents from the two main negotiating tracks running to well over 150 pages, it is highly likely that a shorter, more focussed document will be needed.

As of Thursday evening, it did not appear to exist.

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