Ministers in 12-nation Trans-Pacific trade talks said they had yet to reach agreement on tariffs and other market access issues, with the timing of a completed deal looking increasingly unclear. Ministers said they had made significant progress during four days of meetings in Singapore, but the talks ended with no clear indication of a time frame to clinch the TPP (Trans-Pacific Partnership) agreements. "Market access is in some respects the heart and soul of any trade agreement so until that's done, we don't have an agreement," New Zealand Trade Minister, Tim Groser told a news conference after the talks. The U.S.-backed deal aims to cut tariffs and set common standards on other trade issues across a dozen countries that cover almost 40 percent of the global economy. Long-running differences on tariffs on imported goods, particularly between the United States and Japan, which is keen to protect sensitive products such as rice, meat and wheat, are proving difficult to overcome. Two sets of meetings between the Japanese and U.S. delegations during the talks produced no breakthrough. U.S. Trade Representative Michael Froman said market access for agriculture in Japan remained a "significant" issue but played down the idea that TPP talks might proceed without Japan, the second-biggest economy in the bloc. "All the countries around the table are focused on trying to get that deal done with all 12 countries as part of it," he told reporters on a conference call. Sticking points over intellectual property and the rules for state-owned enterprises and government procurement are also proving difficult. "If you ask whether all outstanding issues have been resolved, it is also a common recognition that they still remain," Japan's Economics Minister Akira Amari said ahead of the final part of the talks. Malaysia's International Trade and Industry Minister, Mustapa Mohamed, said participants were all showing flexibility, but some issues were tough to move on. "There are things which can be done, there are others which cannot be done and we've been telling our partners what is doable and what is not doable," he said. No Date in the Diary There had been expectations that the deal could be concluded in time for U.S. President Barack Obama's visit to Asia in April. It is unclear, however, whether ministers will meet again before the trip. "We've made no further plans at this point in terms of the next meetings," Froman said. Another issue is whether the U.S. government will be able to establish the so-called Trade Promotion Authority (TPA), which will deny U.S. lawmakers the opportunity to amend the TPP agreement. Obama has faced opposition from his own Democratic Party over the matter, while other participating countries are said to be worried that, without the TPA, Congress could make major changes to any deal they come up with. Ministers said TPA had not been discussed during the meeting as it was a domestic U.S. political issue. Expectations that other countries may soon join the talks - Taiwan and South Korea have both expressed interest - were also dismissed as premature. "Right now, all of us are focused on closing among the 12 before we consider taking additional members," said Froman. The full list of countries participating in the talks are the United States, Canada, Japan, Australia, New Zealand, Singapore, Malaysia, Brunei, Vietnam, Chile, Mexico and Peru. (Reuters)