"If there is not a binding accord, there will not be an accord," French President Francois Hollande said in Malta while attending a European Union-Africa summit.
A day earlier US Secretary of State John Kerry made it clear the United States would not sign a deal in which countries were legally obliged to cut greenhouse-gas emissions.
The Paris agreement, he told the Financial Times, was "definitively not going to be a treaty... They're not going to be legally binding reduction targets like Kyoto or something."
The 1997 Kyoto Protocol, which Washington signed in 1998 but never ratified, committed rich nations to limiting emissions, backed by tough compliance provisions.
Defining the exact legal status of the Paris pact, and which provisions - if any - would be legally binding, is one of the toughest issues to be settled in the long-running climate talks.
Earlier Thursday, French Foreign Minister Laurent Fabius, also in Malta, described his US counterpart's remarks as "unfortunate".
"We can discuss the legal status of the agreement," said Fabius, who had met Kerry the previous day.
"But it is obvious that a certain number of provisions must have practical effect," he said.
The UN Conference of Parties (COP21), opening with more than 115 heads of state and government in the French capital on November 30th, aims to secure a deal to stave off catastrophic climate change caused by greenhouse gas emissions from burning fossil fuels.The draft accord being negotiated is divided into a core "agreement", laying out the broad objectives for CO2 reduction and financial aid for developing nations, and "decisions" spelling out how to achieve them.
Negotiations have proceeded from the broad understanding that the "agreement" would have a more binding legal status than the "decisions," which would include voluntary national carbon-curbing pledges subject to revision.
Washington has consistently said it would not commit to CO2-reduction targets within an international framework, but that it would accept legal obligations for other provisions.
"What we support is in fact a partly legally-binding agreement," a US official, who attended pre-summit ministerial talks in Paris, explained this week.
Environmental security council
"The accountability system of the agreement would be legally binding, so (would) transparency provisions," the official, who asked not to be named, told journalists.
"Lots of provisions that circle around the (emissions) targets, but not the targets themselves," he added.
Earlier in the week Hollande called for the creation of an "environmental security council" to verify and enforce measures to be adopted at the summit.
"I hope that binding measures emerge from the agreement in Paris," he told a scientific gathering in the French capital.
The next day, his foreign minister said the idea would not on the table in Paris.
"Our priority is to strike a universal accord," Fabius told journalists.
"During the COP in Paris it is not a provision that will be examined." The European Union and developing countries favour a strong legal framework for the new climate agreement.
In a joint statement this month, French President Francois Hollande and his Chinese counterpart Xi Jinping called for "a Paris accord that is ambitious and legally binding".
The overarching goal of the Paris negotiations, which run to December 11th, is to frame a deal to prevent Earth from warming by more than two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial levels.
Countries most at risk - including low-lying small island states and poor nations in Africa - have called for capping the rise to 1.5 C, saying anything less would result in catastrophic impacts.
Incoming President George W. Bush in 2001 refused to ratify Kyoto partly because emerging economies, especially China, were not given targets.