By Richard Black
Environment correspondent, BBC News website
Transfer of technologies such as solar power is a demand of poorer countries
The year's first round of UN climate talks has ended with delegates talking of a clear split between the visions of developed and developing nations.
Developing countries want big emission cuts from rich nations by 2020, as well as finance for climate protection and more transfer of "clean" technologies.
The top UN climate official said richer nations should show "more ambition".
The talks in Bonn were the first round in a series aimed at reaching a new global deal by December.
This would supplant the Kyoto Protocol, whose targets for cutting emissions expire in 2012.
Earlier in the meeting, President Barack Obama's lead negotiator, Jonathan Pershing, told BBC News that the US would only offer cuts that were "politically and technologically achievable".
The president is looking at measures that would bring US emissions back down to 1990 levels by 2020.
But the EU has already pledged a cut of at least 20% from 1990 levels by that date; and developing countries, backed by environment groups, are calling for the industrialised world to act on recommendations made by the Intergovernmental Panel on Climate Change (IPCC) and make a reduction of 25-40% - some say the science now mandates at least 45%.
Mr Pershing said the US wanted to concentrate on achieving larger cuts but over a longer period of time, saying some of the demands from developing countries were "implausible".
But the calls for stronger action were backed by the executive secretary of the UN climate convention (UNFCCC), Yvo de Boer.
"The numbers being discussed so far are still a significant distance from that range," he said.
"More ambition is clearly needed on the part of industrialised countries."
Campaign groups generally welcomed the fresh US enthusiasm for the process, but warned that much greater carbon cuts and finance were needed.
The US faces some demands for stringent carbon cuts
"We have reached a crossroads, and rich countries get to choose the route we all take," said Antonio Hill, senior policy adviser with Oxfam.
"One route leads us out of today's economic and climate crises and towards a low carbon future.
"The other spells disaster for hundreds of millions of people across the globe."
The charity believes the West should commit about $50bn (£34bn) a year to assist poor countries in preparing for climate impacts.
Some observers contrasted the much smaller sums committed so far against the scale of the resources governments have made available to support beleaguered banks.
"Billions are flowing into recovery packages to save polluting industries and bad banks, but a financial stimulus to protect the UN climate talks from bankruptcy and to help those suffering from the impacts is missing," said Kim Carstensen, leader of WWF's Global Climate Initiative.
Delegates will reconvene in Bonn in June, by which time officials will have drawn up a draft negotiating text.
In an indication of how much negotiating lies ahead, delegates agreed to mount two extra meetings between the June gathering and the December summit in Copenhagen.