The UN's climate summit was heading for meltdown this afternoon with countries unable to agree on emission cuts and blaming each other for the descent towards a humiliating fiasco.

Last-ditch efforts by the UN to get the 120 world leaders to at least commit to hold temperatures to a maximum rise of 2C in the next century were failing, as a series of draft political agreement - each weaker than the last - were circulated among countries.

Delegates listen to speeches during a plenary session at the Bella centre in the closing hours of the Copenhagen summit. Photograph: Jewel Samad/AFP/Getty Images Versions of the overarching political text seen by the Guardian showed that profound disagreements between countries had not been resolved. Only weak, long-term aspirations for an overall global emissions cut of 50% by 2050 and an 80% cut by 2050 for rich countries. These commitments, and the 2C pledge, were assumed to be givens in any deal.

As the draft text reached its sixth version, there were some glimmers of hope, as some nations put more encouraging language into the agreement, including a reference to a limit of 1.5C being supported by the science. But more versions are expected.

Observers said that all numbers and target dates were likely to change over the night as further draft texts were issued, but that the two most serious stumbling blocks were demands from rich countries that developing country should peak their emissions within a few years, and the Kyoto protocol should be abandoned before a new legal treaty was in place.

No commitments were sought for any of the major areas of dispute, such as a mid-term 2020 target to reduce greenhouse gas emissions. The European Union's plan to raise its pledge from a 20% cut to 30% cut in emissions by 2020 was blocked, dashing hopes of prompting a series on increased offers from other nations. The latest text even dropped a deadline for reaching a legally binding treaty by the end of 2010. At the start of the week Gordon Brown was insisting that six months was the maximum acceptable delay.

A financial package intended to raise billions of dollars to help poor countries to adapt to climate change and develop green technology was also in doubt as rich countries declined to guarantee the money, simply affirming that they "supported a goal of mobilising $100bn by 2020".

The lack of ambition and near total absence of commitment from the leaders is a bitter disappopintment for the British prime minister, Gordon Brown, and the UK government which has led worldwide efforts to forge an ambitious, legally binding global agreement to stop the rise in carbon emissions by 2020 and reduce them dramatically in the following 30 years.

Negotiators will now continue to work on individual agreements like deforestation, technology, finance but without strong leadership the chances are that it will take years to complete.

Hopes that Barack Obama would deploy his authority as the leader of the world's largest economy - and his personal political charisma - to try to broker a last-minute deal were also frustrated. A visibly angry Obama told world leaders that it was past time for them to come to an agreement. "The time for talk is over," he said.

But Obama did not offer any new pledges of action - either in increased emissions cuts or clarity on America's contributions to a climate fund for poor countries. He also held the line against China, saying America would not yield on the vexed issue of measuring and verifying emissions cuts promised by developing countries.

"I don't know how you have an international agreement where you don't share information and ensure we are meeting our commitments," he said. "That doesn't make sense. That would be a hollow victory."

Despite being accused of blocking progress, the Chinese prime minister, Wen Jiabao, reminded leaders that developed nations had failed to live up to their Kyoto protocol promises and have now set new emissions targets that fall considerably short of the expectations of the international community.

"It is important to honour the commitments already made and take real action," he said in a defiant speech at the opening of the plenary session. "One action is more useful than a dozen programmes. We should give people hope by taking credible actions."

The British energy climate secretary, Ed Miliband, said: "It's an uphill struggle. It always has been. We are at a critical stage and are happy to keep going. Its a very important moment for the world."

Despite the tough defence of China's actions, Wen said his country would try to exceed its target of a 40% to 45% carbon intensity cut and offered greater transparency of emissions monitoring.

Hugo Chávez, the president of Venezuela, joined other Latin American countries to condemn the way the draft text had been prepared, as well as the "pitiful" sums of money being offered to developing nations during the "fast-start" 2010-2012 period. "$10bn a year is a joke. The military expenditure of the US is $700bn per year," he told the plenary session. "If the climate were a bank it would have been saved already."

The gloomy mood among delegates and observers inside the conference centre reflected the failure to deliver the strong political deal promised by leaders. Today was originally the deadline for a legally binding treaty. Hopes of that vanished months ago, but reaching political agreement in all the major areas in Copenhagen was seen as essential.

But some noted that progress has been made in the past year as a result of the build up of the conference.

Yang Fuqiang of the Worldwide Fund for Nature said, "I don't think Copenhagen is a failure. It has already done more than I expected in terms of narrowing ground on key issues. He praised the agreement on a $100bn climate fund by 2020, the setting of targets by developing nations and the slight closing of differences between China and the US on emissions monitoring."

Jean Ping, chairman of the African Union Commission, said his view of the outcome would depend on how the money is destributed. "There has been progress, but not far enough. We want the [climate] fund to be jointly managed with the African Development Bank. Then the access to the money will be easier than if it just comes through an international institution [such as the World Bank]."