The need for a new global climate deal is "greater than ever", according to developing country delegates speaking at the opening of UN climate talks.
Blocs representing the poorest nations called for intensive talks during the year, leading to agreement on a legally binding treaty in December.
The EU backed the call, re-stating that the conclusion of December's Copenhagen summit had not met its ambitions.
But other industrialised countries do not appear so keen for a new treaty.
The three-day meeting here in Bonn is the first since the Copenhagen summit concluded without the global treaty that many countries had aimed for, instead producing a political declaration known as the Copenhagen Accord.
The US and other rich countries see it as a positive development, but others decry it as a figleaf that detracts attention from the real issues.
Describing Copenhagen as "a total failure", Venezuela's delegation chief Claudia Salerno said the accord would not reduce emissions enough to prevent significant climate impacts on poorer countries.
"My country raised its voice against the misnomer 'Copenhagen Accord' because... it contains proposals for voluntary reductions in carbon emissions that according to scientists would lead to increases in temperature of about 5C (9F)," she said.
"So nobody should be congratulating themselves on that. The urgency we face now is even greater than 2009."
Not all analyses of the Copenhagen Accord's pledges on curbing carbon emissions produce such high estimates for temperature rise, but many of those pledges are far from precise.
Lessons of history
The US - which did not speak during the opening session here - has been the accord's principal champion, saying it "achieves a number of landmark outcomes".
Its written submission to the UN climate convention (UNFCCC) backs "further formalisation of the accord" at this year's summit in Mexico, and says that "it will be difficult to find consensus around alternative proposals that depart from the accord understandings".
These statements have raised the hackles of developing countries, which interpret them as meaning that the US now sees the accord as the central global agreement and is not prepared to engage in anything that goes much beyond it.
"As a well-known politician once said, the one thing we learn from history is that we never learn from history," said Tosi Mpanu Mpanu from the Democratic Republic of Congo, speaking for the Africa Group of nations.
"The Africa Group believes that if we are to avoid a repetition of Copenahgen and repair this damaged process, then we must learn from Copenhagen."
And one of the lessons to learn, he continued, was that breaking away from formal inclusive negotiations and instead focusing on "a secret text put together by a selected few fundamentally broke the trust that is necessary for any partnership that aspires to be succesful and enduring".
Fernando Tudela, the Mexican delegate whose government will host this year's summit, referred to the need for "an authentic process of multilateral negotiations", with many others echoing his call.
Time and money
How and when these negotiations can happen, though, is another matter.
Developing country blocs called for at least three extra meetings this year - and perhaps as many as five - in addition to the regular fortnight in Bonn scheduled for June.
Staging all the extra meetings between the 2007 Bali summit and Copenhagen cost more than $30m (£19.5m), according to the UNFCCC secretariat; and governments would have to provide the money needed to hold another series.
Among wealthy nations, the EU appears the bloc most likely to engage with developing country concerns.
"We all need to frankly assess and examine the lessons learned last time," said Spain's Alicia Montalvo Santamaria, speaking for the EU, as Spain currently holds the presidency.
"The EU recognises the positive outcomes of the Copenhagen conference that gave important political guidance from the highest levels.
"However, the outcome did not reflect the EU's ambitions, and... we remain fully commited to negotiations with all parties in order to conclude a comprehensive global legal framework that allows us to stay below a rise of 2C (3.6F) since pre-industrial times."