The ministers and representatives of the 12 participating countries in the ambitious but controversial Trans-Pacific Partnership (TPP) talks failed to reach a deal on Tuesday after four days of meetings in Singapore, leaving market access as one of the main gaps.

"We have agreed on the majority of the landing zones identified at our last meeting. While some issues remain, we have charted a path forward to resolve them in the context of a comprehensive and balanced outcome," the ministers attending the ministerial meeting here said in statement.

Last December, also after meeting in Singapore, the representatives from the 12 participating countries said they made "substantial progress towards completing the Trans-Pacific Partnership."

"Over the course of this meeting, we identified potential ' landing zones' for the majority of key outstanding issues in the text. We will continue to work with flexibility to finalize these text issues as well as market access issues," they said at that time.

U.S. Trade Representative Michael Froman said on Tuesday that it was a good meeting in Singapore and they were able to make some decision about the majority of the "landing zones" that they identified last December.

"And there are remained issues and we're continuing to work with that, and we have pathway forward for doing so," Froman added.

He figured out that market access issues are among across all the 12 countries and across good, services and government procurement and other issues, and the recent talk in Singapore was "a very important week for engaging on the issues."

The U.S. and Japan held several talks at both ministerial level and working level during the meetings here. Froman on Monday said that the gaps between Washington and Tokyo still remain.

The two sides will continue to meet to work and try to bridge the remaining gaps on all directions, Froman added.

Besides the recent round of TPP negotiation, the two major powers among the participating countries, the U.S. and Japan recently conducted several round of high-level talks, especially on their most divided areas like agricultural products and the auto sector.

Some experts also figure out the U.S. "fast track" as the main obstacle for the ambitious package to be concluded.

Froman said at a press conference on Tuesday that each of the countries has domestic process to go through.

The U.S. team are working closely with Congress and updating the ongoing TPP and the Trans-Atlantic Trade and Investment Partnership agreement (TTIP) negotiation status with the them, and also building support on Capitol Hill for moving forward, he added.

The just concluded TPP talks carried on with its tradition of negotiating behind closed doors. The participants include trade ministers and representatives of 12 countries such as Singapore, the United States, Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru and Vietnam.

The time and venue of the next round of negotiations are not decided yet.

The TPP talks were initiated by Singapore, New Zealand, Chile and Brunei Darussalam in 2005, but dominated by the United States after it joined the talks in 2008. Japan joined the TPP talks last year.

Singapore's Ministry of Trade and Industry said the TPP is " envisioned as a high-quality and comprehensive trade agreement that will go beyond tariff elimination and other traditional trade issues to address emerging challenges faced by modern businesses."

The trade pact is believed to be able to have an impact on regional and world trade, as it involves preferential treatment based on the origin of goods. Endi