Hillary Clinton, who regularly promoted White House efforts to complete a huge trade accord with Pacific Rim countries while she was US secretary of state, came out against the deal on Wednesday.

The apparent flip in position is believed to have represented yet another Clinton break from President Barack Obama as she gears up for an intense 2016 campaign battle for the White House.

The Trans-Pacific Partnership (TPP) signed Monday between 12 nations would be the largest regional trade pact ever, encompassing 40 percent of the global economy and marking one of Obama's key diplomatic and economic achievements.

The hard-won trade deal aims to set the rules for 21st century trade and investment to shape its behavior in commerce, investment and business regulation to TPP standards.

US lawmakers have cautiously welcomed the accord, but it faces intense scrutiny in Congress, which will vote on its ratification in 2016.

Clinton said that given what she knows about the deal it falls short of her "high bar" for creating American jobs, raising wages and advancing US national security.

"As of today, I am not in favor of what I have learned about it," she told public broadcaster PBS in an interview.

"I don't believe it's going to meet the high bar that I have set."

As a result of what she called Republican obstruction to needed investment in infrastructure, education and innovation, "America is less competitive than we should be," she said in a later statement.

"Workers have fewer protections, the potential positive effects of trade are diminished, and the negative effects are exacerbated," she said.

"We're going into this with one arm tied behind our backs."

A White House official said a Clinton staffer did alert them of her shift in position on the trade deal but the official declined to provide details.

Clinton said she was "worried" that currency manipulation provisions were not included in the accord.

"We've lost American jobs to the manipulations that countries, particularly in Asia, have engaged in," she said.

Over time, TPP reduces thousands of small and large tariff and non-tariff barriers on trade between the group, from Japanese auto parts to the US market and US rice to Japan.