Japan has approved export of a high-tech material to South Korea for the first time since imposing tighter curbs last month, but doubled down on political pressure and warned it could broaden restrictions on shipments to its Asian neighbor.

The approval and subsequent warning illustrate how Tokyo is upping the ante in the diplomatic row while at the same time is unwilling to unilaterally stop exports to South Korea.

The dispute, rooted in their wartime past and exacerbated by the recent tightening of curbs on shipments of three high-tech components, has stoked nationalism and raised trade concerns.

Relations between the two worsened late in 2018 as part of a decades-old dispute over compensation for forced laborers during Japan's occupation. South Korea has invoked its difficult history with Japan, which colonized the Korean Peninsula during World War II.

South Korean President Moon Jae-in said Thursday that tighter curbs would undermine Japan's international credibility and accused Tokyo of using its industrial advantage as a weapon against another country.

The latest export approval followed "strict examination," Japanese ministers said, cautioning that Tokyo could consider expanding its controls beyond the three high-tech materials.

"If improper use of exports are found beyond three high-tech materials, we will implement thorough steps to prevent recurrence including expanding application examination," Japanese Industry Minister Hiroshige Seko said.

Seko said Japan does not usually announce each export approval but did so this time after South Korea described ­Japan's recent curbs as an "embargo" on shipments.

South Korean Prime Minister Lee Nak-yeon said Tokyo had allowed the export of EUV photoresists, a chemical crucial for Samsung's advanced contract chipmaking production.

Japan has removed South Korea from the "white list" of countries with fast-track trade status, meaning some exporters may have to go through a lengthy permit application process to ship restricted items to South Korea.

South Korea was scheduled to take a call on its plan to drop Japan from a similar "white list" of countries on Thursday, but trade ministry officials said the plan had been put off until further discussions.