Trade ministers of the U.S. and 11 other Pacific Rim countries have extended talks on an ambitious and controversial trade deal to Sunday, in a bid to seal a final agreement before an October federal election in Canada.

Japanese Economy Minister Akira Amari told reporters on Saturday that he had agreed to a U.S. request to stay for another 24-hour negotiations, but demanded that Washington had to find a way forward on biologics.

"I said there were two conditions for us to accept that proposal: first, this would be the last chance, in other words there had to be certainty of getting a deal on pharmaceuticals; second, because of the schedule, Japan could not accept any further extension," Amari said.

Trade officials originally scheduled to wrap up talks on the Trans-Pacific Partnership (TPP) trade agreement on Thursday, but have not yet worked out major differences in the areas of agricultural market access, rules of origin for autos and intellectual property protections for a new class of drugs known as biologics.

As Canada, the third-largest economy in the TPP framework after the U.S. and Japan, has shifted into federal election campaign mode, trade ministers were under pressure in Atlanta this week to get an agreement before the Canadian federal election on Oct. 19.

While Canadian Prime Minister Stephen Harper is a strong supporter of the TPP, his prospect in the federal election remains unclear.

Tom Mulcair, the leader of Canada's New Democrat Party, which until recently was leading the polls, warned on Friday that the new government he may form will not be bound by any TPP deal signed by Harper if he wins the federal election.

The TPP talks, covering about 40 percent of global economy and believed to be the biggest trade agreement in the world in the past two decades, are entering the final stage after over five years of negotiations. There are only a small number of outstanding issues, but they are generally the most difficult and the most political sensitive.

The big question of whether other TPP countries will agree to the U.S. pharmaceutical industry demands for considerably longer period of data protection for biologics is still up in the air, according to trade observers.

That is perhaps the most contentious issue at the negotiating table and the last hurdle in concluding the trade talks, observers said.

TPP countries have data exclusivity for biologics ranging from five years in Australia to 12 years in the United States before rivals can produce copycat drugs that sell more cheaply.

Pharmaceutical firms in other TPP countries have pushed back the U.S. demand for longer period of data protections, voicing concerns that the U.S. might use it as a vehicle to extend drug company monopolies over expensive biologic drugs.

Trade unions, environmental groups, consumer and heath care organizations across the country have also come together to organize protests against the TPP in front of the Westin Hotel in downtown Atlanta, the site of the TPP negotiations, in the past several days.

"We are very concerned because the TPP has been negotiated behind the doors ... We're concerned about the impact on good jobs in the United States and in other TPP countries ... We're concerned about whether corporations could sue our governments outside our court system," Melinda St. Louis, director of International Campaigns with Public Citizen, a consumer advocacy organization in Washington D.C., told Xinhua.

"Since the beginning of the negotiations, we have made very concrete proposals that have different models of the trade agreement, and those concerns have been largely ignored," St. Louis said. "We think it would be a mistake to conclude the deal now from what we know."

Among the dozens of protestors was Zahara Heckscher, a middle-aged woman, identifying herself as a cancer patient, in a T-shirt reading "I HAVE CANCER. I CAN'T WAIT 8 YEARS!".

"I'm against the TPP because I have breast cancer, and my life has been extended by biological medicines. And I know if the TPP passes with the eight-year monopoly, women around the world won't have access to the latest medicines that could save their lives," Heckscher told Xinhua, holding an IV pole that reads "TPP: Don't Cut My IV".

Heckscher described the U.S. proposal to extend de facto monopolies on biological medicines by up to eight years as a "death sentence clause," because "it will prevent generics and biosimilars for eight years and the price is so high" that women, insurance companies and national health care systems may not be able to actually afford these medicines.

The extended TPP talks suggested trade ministers badly wanted to seal a deal before leaving Atlanta. But even if they could reach a deal on Sunday, the final passage of the TPP in U.S. Congress is far from certain.

The earliest date for a final TPP vote in U.S. Congress would be in February 2016, when presidential nomination contests kick off in early voting states including Iowa and New Hampshire, according to trade experts at Public Citizen.

Several Republican and Democratic presidential candidates have begun attacking the TPP, raising concerns about potential job losses in the United States. As the TPP could become one of the hot-button issues in the presidential campaign, it will be very difficult for U.S. Congress to pass the trade deal next year.

While TPP countries could get another chance to continue negotiations on the sidelines of the Asia Pacific Economic Cooperation (APEC) summit in the Philippines in November, failure to strike a deal in Atlanta could also deliver a major blow to the Obama administration's trade agenda and raise questions about its capability and credibility.

The TPP talks are central to U.S. President Barack Obama's policy of advancing economic engagement in Asia and writing the rules for international trade and investment in the 21st century, but have missed so many deadlines of conclusion.

Obama said last month that he was confident that the ambitious Asia-Pacific trade deal can be completed this year.

The TPP talks involve Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.