Climate Change Secretary Chris Huhne has said the EU is making progress in its bid to secure a "roadmap" to a new climate deal at the latest UN talks.
But it was too early to tell if the talks in Durban, South Africa, would deliver a good deal for the climate, he said, warning "it might all go pear-shaped".
Concerns have been raised that countries could end up settling for a weak agreement that does not tackle global warming, locking in "low ambition" on efforts to cut greenhouse gases and committing the world to temperature rises of more than 2C.
But there were signs of progress after the two week-long talks finally stepped up a gear in the last 48 hours, with US special envoy on climate change Todd Stern saying America supported the EU roadmap towards a new deal.
Europe is calling for the talks to agree a mandate to negotiate a new, legally-binding climate deal by 2015 covering all major economies, in return for the bloc signing up to a second period of emissions cuts under the existing Kyoto treaty.
While the bid is backed by the majority of countries at the climate talks, including some of the most vulnerable to the impacts of global warming, major players including the US and China had opposed the plans.
Mr Huhne said: "We know that more than 120 countries here support our vision of achieving a genuine, overarching, global agreement with a roadmap on how to get there.
"That obviously puts a substantial amount of pressure on countries that are not signed up to our vision and a number of them are beginning to back it and you saw that today with the US coming up and saying it's in favour of a roadmap."
He described the US move as a step forward, but warned: "It's too early to say we're going to be able to achieve a really good deal here. It might all go pear-shaped. It's not a done deal."
And he warned that if Europe did not get a "credible" deal both in terms of the content and timeline for a roadmap, including dates for concluding negotiations, it would not sign up to it, saying: "We're not interested in papering over the cracks. We're interested in something that really does provide us with a roadmap to a single, global, overarching agreement that delivers a solution to climate change."