Tami Overby, vice president for Asia at U.S. Chamber of Commerce, said the delay in sealing the pact was because negotiators were trying to achieve "some really hard things."
"The deadline is not nearly as important as ending up with a comprehensive high-standard agreement," she told CNBC Asia's "Squawk Box" on Monday.
"We started this to be a 21st century agreement and these like-minded countries came in knowing that they're putting everything on the table. Now is the time to put up or shut up," she added.
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Japan's Economics Minister was quoted by Reuters last week as saying that Tokyo could make concession on some sensitive farm products.
The U.S. has urged Japan to end all tariffs in five categories of rice, beef and pork, dairy products, wheat and sugar, according to media reports. Japan meanwhile wants Washington to set a timeline for scrapping tariffs of 2.5 percent on imports of passenger cars and 25 percent on light trucks.
"Every country has their sensitivities and there are ways to approach this – longer phase outs for instance," said Overby. "There are still some hard things to do but there is progress."
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Japan's Prime Minister Shinzo Abe has flagged the TPP as a key part of his agenda to revive the country's growth prospects after years of deflation and lackluster growth. He has faced opposition from Japan's powerful farm lobby to opening up local markets.
— Writing by CNBC's Dhara Ranasinghe. Follow her on Twitter at @DharaCNBC