France has offered a key concession to the US on the eve of historic climate talks in Paris, saying a new global climate accord will not be called a "treaty" and might not contain legally binding emissions reduction targets.

In a significant climbdown, Laurent Fabius, French foreign minister, said signatories to the planned deal would still be legally required to meet many of its terms but most likely not the carbon-cutting goals underpinning the agreement.

Security measures are seen during final preparations for the COP21, Paris Climate Conference site on November 26, 2015 in Le Bourget, France. Patrick Aventurier/Getty Images

"The accord needs to be legally binding. It's not just literature," Mr Fabius told the Financial Times. "But it will probably have a dual nature. Some of the clauses will be legally binding." Mr Fabius, who is to chair the UN climate conference, added: "Another question is whether the Paris accord as a whole will be called a treaty. If that's the case, then it poses a big problem for President Barack Obama because a treaty has to pass through Congress." The comments are among the first by a senior official to signal a willingness to accommodate the world's second largest carbon emitter to achieve a successful deal. John Kerry, US secretary of state, warned in an FT interview this month that the Paris climate change summit could not deliver a treaty that legally requires countries to cut their emissions.

Paris plays host to the biggest UN talks on tackling global warming and curbing emissions since the ill-fated Copenhagen summit in 2009. Negotiators from nearly 200 countries will meet to try and strike the first accord to limit planet-warming greenhouse gas emissions since the Kyoto protocol in 1997. Mr Kerry stressed that there were "not going to be legally binding reduction targets like Kyoto", a reference to the 1997 Kyoto protocol, a UN climate treaty which had targets for cutting emissions that countries ratifying it were legally obliged to meet. The Kyoto protocol was not ratified by the At the time, François Hollande, ​the French president, reacted angrily to Mr Kerry's comments, saying making the accord legally binding was the whole point. If it were not binding "there won't be an agreement because that would mean it would be impossible to verify or control the undertakings that are made", he said.

Many countries are comfortable with both the term "treaty" and legally binding emissions targets. But this would increase the likelihood that the agreement would have to go to a hostile US Congress for approval, an outcome the Obama administration is keen to avoid. Veteran observers have long expected that a final deal would need to be worded in a way that satisfied the US, as well as China and other large emerging economies reluctant to take on onerous legal obligations to cut emissions. The EU and other countries have long said the Paris deal should be an "international treaty" with binding measures to cut emissions. But Mr Fabius said: "It would be pointless to come up with an accord that would be eventually rejected by either China or the US." However, he said there would be a debate over whether a mechanism to review the targets every five years should be voluntary or obligatory.