SEOUL/TOKYO -- Seoul has pointed to its interceptions of illegally exported sensitive materials to discredit Japan's claim that South Korea lacks a proper monitoring regime, prompting an immediate rebuttal from Tokyo, as bilateral relations appear to plumb another low.

Tokyo's export curbs on semiconductor materials, implemented last week, cited a breach of trust by South Korea and "improper" incidents regarding materials it shipped to the South.

Japan's move is widely seen as retaliation for South Korean court rulings ordering Japanese companies to compensate those forced to work for them in World War II.

In response, Seoul brought up its record on crackdowns to insist that Japan's argument has no basis.

There were 156 cases from 2015 to this March of sensitive materials illegally shipped from South Korea to Southeast Asia, China, the Middle East and elsewhere, according to South Korea's Ministry of Trade, Industry and Energy.

Fourteen cases were caught in 2015 and 22 in 2016. The number more than doubled to 48 in 2017, the year Moon took office.

Etching gas, one of materials targeted by Japan's export curbs, was illegally shipped to Vietnam in December 2017 and the United Arab Emirates this January. In addition to semiconductors, etching gas can also be used in the production of nuclear and chemical weapons, including sarin gas.

But Japan remains unconvinced. "Just because South Korea caught some cases doesn't mean it's doing enough," a Japanese government source said. Tokyo continues to question whether Seoul has implemented appropriate screening and other measures to prevent illegal shipments.

South Korea argues that the shipments were made by a handful of domestic companies and do not involve Japan-made etching gas. High-grade etching gas imported from Japan cannot be used for sarin production, which involves lower-grade materials, it says.

Seoul views the recent surge in busts as a sign of a successful crackdown, backed by increased training of police and maritime authorities, and rejects Tokyo's charge of lax controls.

South Korean Foreign Minister Kang Kyung-wha discussed the situation with U.S. Secretary of State Mike Pompeo by phone Wednesday. Kang expressed concerns over the Japanese controls, which she said will disrupt global supply chains and harm not only American companies, but also the global trade order.

The situation is not desirable for South Korea's relations with Japan and their cooperation with the U.S., she said.

Pompeo reportedly expressed an understanding of South Korea's position, which is to push Japan to walk back the curbs and resolve the situation diplomatically.

State Department spokesperson Morgan Ortagus said on Thursday that Washington "would do everything it could to strengthen the relationships between and amongst" Japan, South Korea and the U.S.

South Korea also sent Kim Hyun-chong, second deputy chief of its National Security Office, to Washington on Wednesday to discuss the issue.

Japan requires individual screening of each contract to export materials that can be used for military purposes, unless the destination has been granted preferential treatment. The export restrictions that took effect July 4 put South Korea back on a contract-by-contract basis for three chipmaking materials.

Unauthorized shipments can result in prison time and fines. Particularly flagrant violations are announced to the public.

But South Korea sees Japan as the one falling short. Japan is less transparent because it has not disclosed the numbers of illegal shipments and busts, unlike South Korea or the U.S., it argues.

Export officials from both sides meet in Tokyo on Friday for their first sit-down since Japan announced the export curbs. Japan's minister of economy, trade and industry, Hiroshige Seko, is expected to reject any requests for bilateral negotiations or the lifting of the restrictions.