SEOUL, South Korea — South Korea retaliated against Japan on Monday in a diplomatic and trade dispute between the two key American allies, deciding to remove its neighbor from its list of countries entitled to preferential treatment in trade.

South Korea’s tit-for-tat action had been expected since Japan took a similar action against South Korea on Aug. 2. Still, the move provided Washington with fresh evidence that neither South Korea nor Japan would back down anytime soon, even though President Trump has urged them both to “sit down and get along with each other.”

The removal of Japan from South Korea’s “white list” of 29 most-trusted trading partners will take effect in September, said Sung Yun-mo, South Korea’s minister of trade, industry and energy.

It was not immediately clear how the tightened export controls South Korea and Japan have introduced against each other would affect bilateral trade, because the measures do not ban certain kinds of trade outright. Rather, they simply give the countries a tool to slow down or stop shipments of sensitive goods.