The 12 countries involved in the Trans-Pacific Partnership free trade talks are considering letting members decide their tariff phaseout periods on a bilateral basis instead of adopting a unified rule, sources said.

Such an exceptional approach on tariffs, which could enable each country to retain tariffs on sensitive goods for a longer period of time, is being proposed because the whole negotiation process has been hampered by the Japan-U.S. dispute over whether Tokyo can retain tariffs on its "sacred" five farm products, the sources said Sunday.

The overriding principle behind the U.S.-led TPP is to abolish all tariffs. The 12 members have sought to allow each nation to scrap their tariffs within 10 years, in principle.