Japan and the United States failed to make significant progress Thursday on opening the Japanese automobile sector, ending working-level talks in Tokyo aimed at sealing the 12-nation Trans-Pacific Partnership agreement.

"Though our mutual understanding advanced as a whole, there was no major progress," Takeo Mori, Japan's ambassador in charge of economic diplomacy, told reporters after the talks. The two nations will continue to negotiate but could not set specific dates for their next meeting.

The free-trade talks, attended by Acting Deputy U.S. Trade Representative Wendy Cutler, were aimed at bridging gaps over nontariff measures in the auto sector — one of the major sticking points in the U.S.-led initiative.

Washington has urged Tokyo to crack open the door to its restrictive auto market further, saying that nontariff barriers like regulatory standards are preventing U.S. automakers from expanding sales in Japan.

The countries participating in the TPP talks include Japan, the United States and 10 others, but solving problems between the two biggest economies in the framework is seen as vital to advancing the broader negotiations.