Japan hit back at South Korea on Tuesday for removing Tokyo’s fast-track trade status, with the industry minister saying Seoul has failed to explain its reason for the move, the latest in an escalating trade row.

South Korea on Monday signaled plans to remove Japan from a list of countries with fast-track trade status in September, citing problems with export control measures.

Minister of Economy, Trade and Industry Hiroshige Seko said Seoul has not shown how Japan has fallen short of international export control measures.

“From the start, it is totally unclear under what basis South Korea can say that Japan’s export control measures don’t meet the export control regime,” Seko said on Twitter.

The tighter trade regulations, including potentially lengthy permit application processes, will apply to South Korean exports to Japan.

South Korea plans to split its fast-track category into two and initially put Japan as the only country in the second one, its Ministry of Trade, Industry and Energy said Monday. The move came less than two weeks after Japan removed South Korea from its whitelist of nations considered safe enough to receive exports of strategic materials.

Park Tae-sung, a senior South Korean trade ministry official, added that Japan was designated the first country in the new group because of inappropriate trade practices, but he did not provide details.

Relations between the two countries have soured since a ruling by South Korea’s Supreme Court last year that a Japanese company should compensate South Koreans who were conscripted as forced laborers during World War II.

The dispute has undermined the economic outlook of South Korea, which is already struggling to cope with the U.S.-China trade war. Companies in South Korea need materials from Japan to produce memory chips and displays.

“It’s symbolic, given that the importance of South Korean products in Japan’s industries is small,” said Oh Tae-heon, an economist who teaches Japan studies at Kyung Hee Cyber University in Seoul. “It won’t create the kind of urgency in Japan that South Korea felt when exports of semiconductor materials were curbed.”

South Korea’s trade deficit with Japan was $24 billion in 2018, the biggest among its more than 250 trade partners, according to the Korea International Trade Association.

Industry minister Sung Yun-mo told reporters Monday in a briefing that South Korea is ready to agree to talks with Japan during its 20-day review period before the new designation takes effect in September.

Currently, 29 nations are in South Korea’s “Ga” list of most trusted trading partners for strategic materials, while all other countries belong to the other “Na” category, according to the trade ministry’s website.

Machine tools, chemicals and stainless steel are among the types of products that South Korea’s ministry has listed on its website as subject to the export controls.

Japan would be placed in a new “Ga2” category and treated “in principle” in the same way as countries in the “Na” category, the ministry said in an emailed statement.