Trade ministers from a dozen Pacific nations meeting in Atlanta extended talks on a sweeping trade deal until Saturday in a bid to get a final agreement on the most ambitious trade pact in a generation.

Officials extended talks originally scheduled to wrap up on Thursday in a determined effort to produce a breakthrough on the Trans-Pacific Partnership, which would liberalize trade in 40 percent of the world economy for a region stretching from Vietnam to Canada.

"No-one wants to leave without an agreement," Mexican Economy Minister Ildefonso Guajardo told Reuters after a second plenary session of top officials from all 12 nations. "The good news is that we will not leave here without one."

Observers pointed to progress on autos, Canada's pledge to compensate farmers hurt by imports and signs of a possible compromise on patent protection for new drugs as evidence of advancement.

"We are starting to see the path to an agreement and have agreed to make final efforts," Japanese Economy Minister Akira Amari told reporters, although conditions were still difficult.

Several officials said a final deal could come quickly if key issues -- intellectual property protection for medicines and trade in dairy and autos -- are cleared in remaining talks.

The alternative would be for ministers to try to reconvene in November, although that risked losing momentum in a process that has already run five years.

A deal would be a legacy-defining achievement for U.S. President Barack Obama. But the trade deal is seen as a threat by an array of interest groups from Mexican auto workers to Quebec dairy farmers to cancer patients who worry that it could push the cost of new therapies out of reach.

Congressional concerns

In a reassertion of concern in Congress, a group of U.S. lawmakers from both parties sent a letter to U.S. Trade Representative Michael Froman and Treasury Secretary Jack Lew on Wednesday.

"We urge you to take the time necessary to get the best deal possible for the United States, working closely with us," said the letter signed by House Ways and Means Committee Chairman Paul Ryan and Senate Finance Committee Chairman Orrin Hatch as well as the senior Democrats on those two committees.

Several Republicans attacked a new U.S. proposal to ensure governments would be free to enact anti-smoking measures without fear of legal action by tobacco companies.

That could prevent companies like Philip Morris and Japan Tobacco Inc from using rules to protect foreign investors to challenge public health measures but falls short of the sweeping measure anti-smoking groups had hoped for.

Guajardo said talks on auto trade had progressed but were not over yet.

The auto issue is crucial for Japan, whose automakers, led by Toyota Motor Corp, depend on sales to the U.S. market and want flexibility on sourcing auto parts.

But Mexico, which has experienced a boom in auto-related investment over the last two decades, wants to protect its manufacturers against increased competition from Asia.