The EU and small island states have criticised the US for saying the target of keeping global warming below 2C should be removed from climate talks.
At the 2010 UN climate convention meeting, governments agreed to take “urgent action” to meet the target.
But last week the chief US climate negotiator Todd Stern said insisting on the target would lead to “deadlock”.
Spokesmen for the EU and the Alliance of Small Island States (Aosis) said the US should stick to promises made.
“Suddenly abandoning our agreement to keep global warming below 2C is to give up the fight against climate change before it even begins,” said Tony de Brum, Minister in Assistance for the Marshall Islands.
“‘Flexibility’ on our 2C limit would set the world on a path to irreversible, runaway climate change.
“For many low-lying island states, including my own, that is not a solution – it is a death sentence,” he told BBC News.
Isaac Valero-Ladron, the EU’s climate spokesman, said governments including the US had to live up to prior promises.
“Also, consolidated science continues to remind us of the dire consequences of going beyond such a temperature increase,” he said.
The core objective of the UN climate convention (UNFCCC), agreed in 1992, is to prevent “dangerous” climate change.
Scores of governments believe that 2C is a realistic indication of where “dangerous” climate change begins, although a greater number – principally those highly vulnerable to impacts such as sea level rise – say even 2C is too high. More