Trade talks between the United States and Japan failed to produce a breakthrough Thursday, in yet another blow to the Trans-Pacific Partnership free trade agreement.

The unwieldy trade pact is a major priority for the Obama administration, but progress has stalled after 20 rounds of negotiations spread over a period of years have failed to produce a consensus.

The latest hang-ups are over Japan's efforts to protect agricultural products including beef, rice, sugar and pork. In the same vein, Washington is hoping to protect U.S. automakers from Japanese competitors.

Advisers from both countries had been engaged in negotiations in the lead up to President Obama's trip to Japan, and analysts suggested that if significant progress were made, details would be announced at Thursday's joint press conference.

Yet no breakthrough materialized, leaving both leaders to say only that the initiative remains a priority and talks will continue.

"We are closer to agreement on issues like automobiles and agriculture," Obama said. "Now is the time for bold steps that are needed to reach a comprehensive agreement, and I continue to believe we can get this done."

Twelve countries -- Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the U.S. and Vietnam -- are taking part in the TPP talks. Together they make up 40% of the global economy.

The agreement has the potential to knock down tariffs and import quotas, and open new Pacific markets to American companies. The U.S. and Japan -- the first and third largest economies in the world -- anchor the deal, which does not include China.

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Yet the TPP remains highly controversial in many of the countries currently involved in negotiations.

Key members of the U.S. Congress say they are being kept in the dark about pact details, and some members of the president's own party have voiced concern over the treaty's impact on jobs.

Significant political opposition makes it unlikely that Obama will be able to push any agreement through Congress before the 2014 mid-term elections.

Analysts at the Eurasia Group said that Japanese Prime Minister Shinzo Abe is well aware of this dynamic, making concessions unlikely in the near term.

" [Abe] thus has little incentive to respond to U.S. demands that Japan open its agriculture, services, and auto sectors before Obama can ensure speedy U.S. ratification," the analysts wrote in a recent report.