The US demand for longer patent protections for drugs has bogged down talks on the Trans-Pacific Partnership for another day.
With the top-level negotiations to finalise the huge trade agreement already extended two days, Washington's partners in the 12-country talks are resisting the US push for much more than the widely accepted five-year patent protections.
The US, which has a 12-year standard domestically to protect the creations of pharmaceutical companies, was said to be willing to compromise at eight years, but Australia, Chile and Peru at least have resisted the push.
Australia, which has five-year patent protection for the drugs, has said the US stance challenges its public health policy.
The issue is one of the last to be settled in the long-running TPP negotiations, along with still-sticky talks on freeing up markets for New Zealand and Australian dairy exports, a particularly sensitive challenge to Canada.
Successful negotiations could lead to the creation of the world's largest free-trade pact, covering 40 percent of the world's economy.
The partners - which also include Japan, Singapore, Vietnam, Brunei, Malaysia and Mexico - have already agreed on a broad range of issues, from handling foreign investor disputes to weakening protections for state enterprises to lowering barriers to trade in textiles and farm goods.
The trade ministers and other top officials in the talks were ready to let them spill over into Sunday but not beyond, according to officials involved.
A number had their eyes on their travel schedule: the G-20 group of leading economies is holding a meeting of trade ministers on Monday and Tuesday in Istanbul.
They had entered the talks on Wednesday under pressure to strike a final deal, after their talks in Hawaii two months ago failed.
The final issues included how much Canada and Mexico, privileged suppliers of auto parts to the US car industry under the NAFTA trade treaty, would allow that market to open up to Japanese car parts from other countries such as China and Thailand.