Will the ambitious Transatlantic Trade and Investment Partnership, the world's largest trade pact, ever see the light of day?

After leaks from the closed-door negotiations surfaced Monday, a deal between the Americans and the Europeans looks less likely as skepticism over the agreement grows on both sides of the Atlantic.

Engaged in tough trade negotiations since mid-2013, the United States and the European Union tried to downplay the trove of TTIP documents put online by Greenpeace, describing them as "misleading" and deploring "wrong" interpretations of them.

But the fact remains: Despite the efforts of US President Barack Obama, who wants to clinch the trade deal by the end of the year, success is looking increasingly unlikely.

A halt in the TTIP negotiations is "the most probable option," a top French trade official said on Tuesday, blaming Washington for the impasse.

Given France's weight in the EU, "there cannot be an agreement with France, and much less against France," said Matthias Fekl, a junior minister responsible for representing Paris in the talks.

Edward Alden of the Council on Foreign Relations, a US think tank, said the most striking element of the leaked documents was that it showed "the two sides are still so far apart in the negotiations, that there are such big issues that remain unresolved."

With the TTIP, the United States and the 28-nation European Union want to topple regulatory and tariff barriers to trade and investment.

There are plenty of thorny issues to tackle, from market access to opening up the EU services sector and improving European access to US government procurement projects.

Negotiators wrapped up the 13th round of talks in New York on Friday said they had made progress in the talks, as is customary.

But there was a sense of irritation on the European side about the US refusal to open access to its public procurement.

"We need to reach a similar level of progress in market access procurement as we have already done in tariffs and services in order to move the negotiations towards the endgame," said Ignacio Garcia Bercero, chief negotiator for the European Commission.

- 'A period of tremendous uncertainty' -

The clock, however, is ticking. An ardent defender of TTIP, Obama will leave the White House in January and his successor, who will be elected in November, could be less inclined to promote free trade -- an issue that has fallen out of favor with a public distraught over jobs lost overseas.

The situation is hardly less politically sensitive in Europe where there are deep suspicions that the deal will erode ecological and health regulations to the advantage of big business.

"If the deal cannot be concluded under the Obama administration, further progress in the talks likely will have to wait after the different European elections in 2017," said Harvard law professor Mark Wu, a former official at the US Trade Representative which is representing Washington in the negotiations.

Next year, general elections will be held in both Germany and France, where debate over the TTIP is intense and could feature in their respective campaigns.

French leaders appear to have already given in to skepticism, after a week in which Prime Minister Manuel Valls and President Francois Hollande toughened their tone and pledged to oppose any accord that lacks guarantees on quality standards for health, the environment and French agriculture, among other issues.

Germany also has ratcheted up pressure, predicting the proposed deal "will fail" if Washington refuses to make concessions in the protracted talks.

And the possibility that Britain could decide to leave the EU in a June 23 referendum is yet another cloud hanging over the talks.

"It's a period of tremendous uncertainty for trade policy in both the US and Europe," said Alden.

- 'Leaks to embolden opponents' -

The Greenpeace leaks, meanwhile, risk ossifying positions further, particularly among the public.

"The leaks will embolden opponents of the deal and make it harder to try to bridge these differences," Wu said.

After the documents emerged, US environmental group Sierra Club came out against the treaty, saying it was "heading in the wrong direction and would put President Obama's trade policy on the wrong side of history."

And Washington activist group Public Citizen said the leaks show "business will gain enormous power to block, slow, undermine and repeal European regulations."

The leaks are not the first hiccup for the TTIP, which in 2014 was hit by revelations that the US National Security Agency was spying in Europe.

But they could end up lowering ambitions for the pact, even though Washington and Brussels have said they opposed any "TTIP light."

"Both sides will see a TTIP light as preferable to a complete failure of the negotiations," Alden said.