"Shortly before, I received a report from (Economics) minister (Akira) Amari that the TPP negotiations reached a broad agreement," Shinzo Abe told reporters at his official residence, broadcaster NHK reported on its website.
A US official in the city of Atlanta, where the negotiations were being held, confirmed the agreement.
Amari is leading Japan's delegation in what has been five days of gruelling talks bogged down in disagreements, especially over the international dairy trade.
Yesterday Amari had indicated they were close to grasping a deal, but a press conference planned for that day was called off.
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The TPP is an ambitious idea pushed hard by the administration of President Barack Obama to create a free-trade area that would address "21st century trade issues" such as intellectual property protections, digital trade rights and protections for investors.
The Obama administration also hopes that China, the world's second-largest economy, would eventually be forced to accept the standards locked into place by the TPP, especially if other countries like South Korea join it as expected.
Already once this year, in July in Hawaii, trade ministers gathered with expectations of a deal -- and left empty-handed.