The minister in charge of the Trans-Pacific Partnership free trade negotiations said Sunday that Tokyo can make no more concessions to Washington on sensitive issues after a Japan-U.S. meeting ended without progress.

"We had a very tense discussion on outstanding issues, but we reached no conclusion," Akira Amari told reporters after meeting with U.S. Trade Representative Michael Froman in Tokyo, suggesting they focused on tariffs on farm products.

He declined to elaborate, saying the negotiations are confidential.

The meeting came in the lead-up to ministerial talks slated for Dec. 7 to 10 in Singapore. While the 12 Pacific Rim negotiating countries are aiming to reach a deal by the end of December, it is uncertain whether the deadline can be met as differences between Japan and the United States remain a huge hurdle.

While the U.S.-led TPP aims for the abolition of all tariffs, Japan wants to retain tariffs on five farm product categories, including rice. The United States and other TPP members are putting strong pressure on Japan to further open up its agricultural market.

Chief Cabinet Secretary Yoshihide Suga and farm minister Yoshimasa Hayashi also attended the meeting to show the country's firm stance, while Ambassador Caroline Kennedy was included on the U.S. side.

Amari said Tokyo and Washington will continue negotiations to bridge their differences before the gathering in Singapore.

Froman also met with Minister of Economy, Trade and Industry Toshimitsu Motegi later Sunday.

At the outset of the meeting, Froman said he is "confident" they will be able to resolve remaining issues if both sides show good faith.

Motegi told reporters following the meeting that Japan has done its utmost to make concessions on tariffs related to products that the United States regards as sensitive, urging Washington to show "flexibility" on contentious issues.