Japan's tariffs on key agricultural products may be lowered as a result of entering the Trans-Pacific Partnership negotiations, Liberal Democratic Party Secretary General Shigeru Ishiba hinted Saturday.

Speaking on a TV program a day after Prime Minister Shinzo Abe announced Japan will join the U.S.-led free-trade talks, Ishiba also said the ruling LDP plans to designate five items — rice, wheat, beef and pork, dairy products and sugar — as exempt from tariff abolition in its campaign platform for this summer's Upper House election.

Abe promised Friday that his government will seek to win exemptions for certain farm products deemed critical to the domestic agricultural industry. The TPP in principle requires the elimination of all trade tariffs among member countries.

But Ishiba underscored the difficulty of maintaining all of the current tariff barriers for the five items, saying: "The thrust of the (TPP) negotiations is how to protect products such as rice, wheat, beef and pork. It does not result in the argument that the tariffs cannot be lowered even by 1 percent."

He also denied that joining the negotiations violates a pledge the LDP made while campaigning for December's Lower House election to oppose Japan's entry to the TPP talks as long as it was premised on scrapping all tariffs without exception.