US senators agreed to open the debate on legislation that could allow Obama to seal the 12-nation Trans-Pacific Partnership (TPP), set to be the biggest trade deal since the 1995 North-American Free Trade Agreement (NAFTA).

On Tuesday, all but one Democrat in the Senate had blocked a decision to move forward with the debate on a package of trade issues, embarrassing the president, who is also a Democrat.

Under Wednesday's agreement, the Senate agreed to tweak the package that failed in Tuesday's procedural vote. The impasse involved side issues including a proposal to punish countries that keep their currency artificially low to boost exports.

There will now be a stand-alone vote on a customs enforcement bill that includes "currency manipulation" sanctions as early as Thursday.

Senators are hoping to then discuss whether to approve "fast-track" negotiation powers, which Obama has argued are essential for him to push through TPP.

It would allow him to submit a trade accord to Congress for a yes-or-no vote with no amendments. Obama's TPP negotiating partners in Asia and South America have said they want to see fast-track legislation enacted before finalizing the pact.

TPP has strong Republican support, but most Democratic lawmakers oppose free-trade agreements, saying they jeopardize US jobs. Senator Elizabeth Warren, a prominent leader of the party's left wing, has been particularly vocal about the issue, exposing a deep rift between her and the president.

The countries taking part in the TPP negotiations are the US, Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore and Vietnam.

ng/cjc (Reuters, AP)