A key issue is Japan's request that South Korea reduce the number of South Korean long-liners that can catch cutlassfish in Japan's exclusive economic zones by 133 from the current 206, a demand rejected by South Korea.

   South Korea said Japan violated their 2015 deal, in which South Korea agreed to cut the number of its long-liners by 40 by 2019 from 206.

   Seoul said it cannot accept Japan's changed position due to the strong opposition of South Korean fishermen.

   The development comes as bilateral relations plunged to their lowest levels in recent decades over a trade row stemming from Japan's wartime use of Koreans as forced labor during its 1910-45 colonial rule of the Korean Peninsula.

   Japan has imposed tighter regulations on exports to South Korea of three materials -- resist, etching gas and fluorinated polyimide

-- that are critical for the production of semiconductors and flexible displays.

   Japan also removed South Korea from its "whitelist" of trusted trading partners in retaliation against last year's South Korean Supreme Court rulings ordering Japanese firms to compensate South Korean victims of forced labor.

   On Wednesday, South Korea filed a complaint with the World Trade Organization over Japan's export curbs, upping the stakes in the unprecedented trade row between the two Asian neighbors.

   South Korea and Japan are close economic partners and key allies of the United States, though they have long been in conflict over territory and other historical disputes.