China is attempting to scupper chances of a comprehenive agreement at the Copenhagen climate summit by using delaying tactics, sources inside the negotiations have told The Independent.

At an emergency meeting convened at the Bella Center this morning, Barack Obama and Gordon Brown assembled 26 heads of state in an attempt to revive a deal. But China's Premier Wen Jiabao did not attend and was replaced by vice foreign minister He Yafei.

This afternoon, the US president and his secretary of state Hillary Clinton called another meeting with China, but were snubbed again when only three low-level Chinese delegates arrived.

According to a high level source, the US president clearly regarded Premier Wen's absence as a major diplomatic insult, and snapped: "It would be nice to negotiate with somebody who can make political decisions."

The leaders are currently negotiating on a draft text which say the world should aim to halve greenhouse gas emissions by 2050 from 1990 levels, according to a new draft text at a UN climate summit that makes concessions to developing nations and small island states.

"We agree that deep cuts in global emissions are required...with a view to reduce global emissions by 50 percent in 2050 below 1990 levels," it says.

The halving target was new compared to earlier drafts at a summit of 120 leaders on Friday, the finale of two years of negotiations on a new deal to fight global warming.

The draft retained plans to limit a rise in world temperatures to 2.0 Celsius over pre-industrial times but added a review in 2016 that would also consider a tougher limit of 1.5 Celsius.

About 100 nations including small island states and least developed nations, mostly in Africa, want to limit world temperature rises to 1.5 Celsius, saying they are most at risk from droughts, shifts in Monsoon rains and rising sea levels.

The draft "Copenhagen Accord" retained plans for new aid for developing nations of $10 billion a year from 2010-12, rising to $100 billion a year from 2020 to help developing nations.

UK diplomatic sources later confirmed that China had taken huge offence at remarks by President Obama over the need to independently monitor every country carbon emissions. In his speech President Obama said: "Without any accountability, any agreement would be empty words on a page". The Chinese delegation interpreted these comments as an attempt to humiliate them. It prompted Prime Minister Wen Jiabao to return to his hotel and send low level delegates to take his place in the talks.

Diplomatic efforts were underway late this afternoon to try and bring the two leaders face to face for a second round of talks to patch up the disagreement.

From the Press Association: The news came after Barack Obama warned today that the chance of a global climate change deal "hangs in the balance" as he joined other world leaders at deadlocked talks in Copenhagen.

But the US president offered no new commitments on emissions targets which many hoped for to end the impasse after two weeks of tortuous negotiations.

In a speech to the conference, before leaders including Prime Minister Gordon Brown were due to reconvene a tense meeting aimed at producing a political agreement, he said their capacity to do so appeared to be in doubt.

In an appeal to fellow leaders to find a solution, he said: "The question before us is no longer the nature of the challenge; the question is our capacity to meet it.

"For while the reality of climate change is not in doubt, I have to be honest, as the world watches us today, I think our ability to take collective action is in doubt right now and it hangs in the balance."

A British official at the talks said the prospects of securing agreement were "not great" but Mr Brown was committed to staying until "the very last minute" to secure a deal.

The Prime Minister was optimistic last night about the chances of getting agreement today but hopes were dashed this morning amid ongoing divisions between the 192 countries attending, with China's resistance to verification of its efforts to reduce emissions being blamed for the failure to progress.

Mr Brown has now been asked to bring leaders together over the issue of a proposed 100 billion dollar-a-year long-term finance package for the poorer nations worst hit by global warming.

The US signed up to the plan yesterday and it has support from the EU and African nations but it is contingent on securing a wider deal on issues including verification.

The official said: "The Prime Minister is engaged in tough, long and intense negotiations and is fighting hard for a deal though the prospects are not great.

"A number of key countries are holding out against the overall package and time is not on our side.

"The Prime Minister is committed to doing all he can until the very last minute to make this deal happen but others also need to show the same level of commitment." Mr Obama insisted that the actions the US was taking, including cuts of 17 per cent on current levels by 2020, were "ambitious" and were being taken in the interests of America's economy and security, as well as to tackle climate change.

Laying out what he believed should be in a deal, the president said all major economies needed to take na

tional action to reduce emissions, and there must be mechanisms to review and exchange information on the steps taken - which need not be "intrusive or infringe on sovereignty".

But he said that without accountability on actions to cut emissions, any agreement would be "empty words on a page".

He said: "I don't know how you have an international agreement where we are all not sharing information and ensuring we are meeting our commitments. That doesn't make sense. It would be a hollow victory."

He reiterated America's commitment to a 10 billion US dollar-a-year "fast start" package and long-term funding to the tune of 100 billion US dollars a year by 2020.

And he urged leaders to work together rather than fall back into discussions and debate that had gone on for decades.

"We know the fault lines because we've been imprisoned by them for years. But here is the bottom line: we can embrace this accord, take a substantial step forward, and continue to refine it and build upon its foundation.

"We can do that, and everyone who is in this room will be a part of an historic endeavour - one that makes life better for our children and grandchildren.

"Or we can again choose delay, falling back into the same divisions that have stood in the way of action for years.

"And we will be back having the same stale arguments month after month, year after year - all while the danger of climate change grows until it is irreversible," he warned.

Addressing the high-level conference, Chinese premier Wen Jiabao insisted his country took the issue of climate change very seriously and has made, and would continue to make, "unremitting efforts to tackle this challenge".

He said that its target to curb greenhouse gas growth - to reduce the amount of emissions per unit of GDP by 40 per cent to 45 per cent by 2020 - came without any conditions attached and the Chinese would honour it.

And he said: "We remain fully committed to achieving and even exceeding the target."

He added China would increase the transparency of the actions it was taking to curb its emissions growth.

The key issues dividing rich and developing countries include who should cut their emissions and by how much, the scale of finance to help the poorest nations fight climate change and monitoring of each country's greenhouse gas reductions.

Today is the final day of the two-week summit, which has been mired in wranglings and walk-outs, meaning negotiators were unable to produce an agreed text for the arriving leaders to discuss.

They were locked in talks until 2am today but by the time the conference reconvened, last night's optimism about a possible deal evaporated as it became clear there was still no sign of progress.

Mr Obama, who flew in to join the summit this morning, had been tipped by senior figures to arrive with further commitments from the US, perhaps a rise in its harmful emissions reduction target from 17 per cent on present levels.

Shortly before his speech, he joined the end of a two-and-a-half-hour session of talks which broke up while fresh efforts were made to draft an agreement acceptable to all sides.

Around 30 of the key players locked themselves into a room without advisers for a fresh effort to find a way forward as the scheduled end of the conference loomed.