TOKYO, March 27-- Japanese Prime Minister Shinzo Abe would disappoint U.S. President Barack Obama over the U.S.-led Trans-Pacific Partnership (TPP) free trade talks as the Japanese conservative leader said Friday that his country would not make easy concessions on accelerating the negotiations. "It is impossible to make unnecessary concessions in line with my trip to the United States," Abe told a Diet session, adding that the TPP free trade talks are "in the final phase, but problems remain".

The prime minister made the remarks ahead of his eight-day visit to the United States from April 26, and he will visit the White House on April 28 to have a summit with Obama who is eager to conclude the marathon TPP talks at an early date so as to leave positive legacy for his Democrats in future presidential elections.

Japan is reluctant to open its agriculture market, particularly on rice and pork, to inexpensive U.S. products, while the United States is considering that when it will remove its tariff over Japan-import cars. The Lingering differences between the two major economies in the 12-member bloc are regarded as a drag on the whole negotiations.

Abe's comments undoubtedly cast shadows over the conclusion of the talks. However, U.S. Trade Representative Michael Froman on Thursday expressed his confidence of an early deal. "We do feel that we can close this out in a very small number of months," he said in Washington.

Obama visited Japan in April last year with an ambitious plan to push forward their TPP-related talks. The president sought to acquire Japan's concession by reiterating U.S. defense commitment to its ally over disputed islets with neighbouring countries.

Abe's U.S. trip will also make him the first Japanese leader to address the Congress on April 29. "His address will provide an opportunity for the American people to hear from one of our closest allies about ways we can expand our cooperation on economic and security priorities," John Boehner, House of Representatives speaker, said in a statement.

However, regarding the Japanese leader's historical revisionism, a group of U.S. World War II soldiers and their relatives have said Abe should only be invited to Congress for a speech if he admits Japan's historical responsibility for its wartime conduct, according to Japan's Kyodo News.

The well-known rightist leader set up an expert panel to provide advices to shape his statement for the 70th anniversary of the end of WWII, and the majority of the 16-member panel argued that the word of "aggression" should not be used in the statement as there is no world-recognized definition of "aggression."

Rightist and historical revisionism politics walked by Abe increasingly prompted concerns from its neighboring China and South Korea and prominent world leaders, including German Chancellor Angela Merkel and UN chief Ban Ki-moon, who have urged Japan to face up to its wartime atrocities.

Continuously frayed ties between Japan and its neighbors also forced Washington on Thursday to emphasize that Japan should approach history issues"in a way that promotes healing and reconciliation." The Tokyo's key ally expressed its disappointment over Abe's Yasukuni visit in 2013.

Calling as the corner stone of Japan's diplomacy, Japan-U.S. defense alliance is also rocked by the thorny issue of the U.S. Futenma airbase relocation plan. Japan's southernmost island prefecture of Okinawa, where the U.S. base is located, ordered Monday to suspend underwater work in the Henoko coastal area in Nago city in the prefecture for the base's replacement.

Okinawa Governor Takeshi Onaga warned that if the Okinawa Defense Bureau does not follow the order, the Okinawa government would revoke in a week its permit granted to the bureau for rock drilling at the site. But the Japanese central government neglected the prefecture's demand.

The Okinawa Times editorial chief said recently that the Okinawa government and the central government are facing overall confrontation and situation has never had in local governments in postwar era, adding the central government's tough means is triggering more concerns.

The relocation plan of the U.S. airbase has for long troubled the Japan-U.S. alliance and relations between the prefecture and the Japanese central government. Anti-U.S. base sentiment is deep in Okinawa that holds a bulk of U.S. bases in Japan. The issue will also weigh on Abe's U.S. journey.