U.S. President Donald Trump again criticized Japan over ongoing tariff negotiations on Sunday, but said it is "changing" its way "very rapidly" in the talks with the United States.

Trump was speaking to reporters at Joint Base Andrews near Washington, but did not elaborate on the hint that Japan may have made concessions in the tariff talks.

Earlier, the U.S. president lamented what he has alleged are Tokyo's unfair trade practices.

"We sell them no cars because they won't accept our cars, and they won't accept much of our agricultural stuff," he said.

Trump said in a letter addressed to Prime Minister Shigeru Ishiba last week that his administration will impose a 25% reciprocal tariff on all imports from Japan, effective on Aug. 1.

In response, Ishiba stressed that his government will not make concessions easily in order to protect his country's national interests. Japan had aimed to reach a trade agreement with the United States at a summit of their leaders in June, but talks have been stalled.