Low-cost carrier Air Seoul Inc. plans to soon close half of its 12 offices in Japan after suspending some flights in the face of frayed Japan-South Korea ties, sources close to the matter said Monday.

Air Seoul will shut offices in Hokkaido, Shizuoka, Toyama, Yamaguchi, Kumamoto and Okinawa prefectures after a sharp drop in South Korean travelers led it to suspend flights connecting the six prefectures and Seoul in September, the sources said.

Air Seoul, a wholly owned unit of South Korean carrier Asiana Airlines Inc. established in 2015, has operated 10 routes connecting Japan and Seoul, including those currently suspended.

The Asian neighbors' ties have sunk to their lowest level in years after Japan in July tightened export controls on certain products to South Korea, which Seoul views as retaliation for court rulings ordering Japanese firms to compensate groups of South Koreans for wartime labor.

The number of South Korean visitors to Japan plunged 58.1 percent in September from a year earlier to 201,200, following a 48.0 percent tumble in August, according to the Japan Tourism Agency.

Asiana Airlines and Korean Air Lines Co. have also suspended or reduced flights, while Peach Aviation Ltd., a subsidiary of ANA Holdings Inc., became the first Japanese carrier to cut services in response to the reduced number of trips by South Koreans.