Paris: France on Tuesday took aim at a vast but controversial EU-US pact to create a free-trade zone covering 850 million people, with President Francois Hollande threatening to veto it as it stands.

Hollande warned that Paris would reject the Transatlantic Trade and Investment Partnership (TTIP) "at this stage" because his country opposes "unregulated free trade."

"Never would we accept the undermining of the essential principles of our agriculture, our culture, of mutual access to public markets," Hollande told a left-wing political conference.

Earlier Tuesday, a top French trade official warned that the talks could grind to a halt because of Washington`s reluctance to make concessions.

"In view of the United States`s state of mind today, that seems to be the most likely option," chief French trade negotiator Matthias Fekl told French radio when asked if the TTIP talks, which began in 2013, could stop.

Given France`s weight in the EU, "there cannot be an agreement without France, and much less against France," said Fekl.

The French comments reflect deep suspicion in Europe that the deal will erode ecological and health regulations to the advantage of big business.

Washington and Brussels want the mega-deal completed this year before US President Barack Obama leaves office, but it has faced mounting opposition on both sides of the Atlantic.

Following the comments from French officials, the Obama administration on Tuesday reaffirmed it was optimistic about concluding the trade deal despite differences in positions in the ongoing negotiations.

"We are confident that we are on track to deliver a high-standard TTIP that reflects the interests and democratic values of both the US and EU, and makes common-sense updates to our existing economic relationship," Trevor Kincaid, a spokesman for the US Trade Representative (USTR) which is leading the US negotiations, told AFP.

"It`s important to remember that we are still in the middle of a negotiation, and that both sides are still working to bridge differences," he said.

On Monday, environmental pressure group Greenpeace released a trove of leaked documents about the closed-door negotiations, charging that a deal would inflict a dangerous lack of standards on US and European consumers.

However, the European Commission, which negotiates trade deals on behalf of the 28 EU member states, said Greenpeace was "flatly wrong" in its interpretation of the documents.

The Greenpeace leak was a "storm in a teacup," Brussels said.

US officials also hit back Monday at the Greenpeace leaks, with the USTR saying: "The interpretations being given to these texts appear to be misleading at best and flat out wrong at worst."

Fekl, France`s top trade negotiator, said Tuesday that Europe was pushing for "reciprocity."

"Europe is offering a lot and we are getting very little in return. This is unacceptable," he said.

"It is a deal that -- in the state it is in today -- would be a bad deal."