WASHINGTON – With U.S. President Barack Obama’s visit to Tokyo approaching, Japanese and U.S. trade chiefs are set to face off again in Washington as they strive to break a deadlock in talks on a massive free trade zone in the Pacific region.

Trade observers say it is necessary to achieve an outcome, or at least to try to make progress, at the April 24 summit between Obama and Prime Minister Shinzo Abe, as failure to overcome differences on outstanding trade issues would significantly undermine Obama’s trip to Japan as a state guest — which many see as a possible impetus for the stalled negotiations.

Trade officials from both countries held a preparatory session Tuesday in the U.S. capital for the ministerial talks on the thorny issue of tariffs on agricultural produce in the Trans-Pacific Partnership negotiations.

“We’re climbing the mountain little by little” even though a big gap remains, Hiroshi Oe, Japan’s deputy chief TPP negotiator, told reporters following a meeting with Wendy Cutler, acting deputy U.S. trade representative.

It remains highly uncertain to what extent the two countries can move closer on outstanding issues at a series of planned meetings between Akira Amari, minister in charge of TPP talks, and Michael Froman, U.S. trade representative, likely to last until Friday, as they remain far apart after their 18-hour talks held in Tokyo last week.

The envisioned TPP initiative, led by Washington, has been deadlocked due mainly to disagreements between Japan and the United States, the two largest economies in the pact.

The United States has urged Japan to open up its agricultural market, but Japan is fighting to protect tariffs on its “sacred” farm product categories, including beef and pork, dairy products and wheat.

Washington, which had long called on Tokyo to stick to the basic TPP principle of abolishing all tariffs, gave up on doing so, and it is now asking Tokyo to lower its tariffs on beef — one of the main U.S. interests — to below 10 percent, according to negotiation sources.