Japan and South Korea are both democracies, market economies and US allies, but their relationship has been strained for decades as a result of Tokyo's brutal 1910-45 colonial rule over the Korean peninsula.

Around 780,000 Koreans were conscripted into forced labour by Japan during the 35-year occupation, according to data from Seoul, not including women forced into sexual slavery by Japanese troops.

In a landmark ruling in 2018, the Supreme Court ordered Mitsubishi Heavy Industries to pay compensations to a handful of the victims, but the Japanese firm refused to follow the verdict.

And earlier this month, the surviving families of four of the victims asked the court to seize Mitsubishi's bonds in South Korea, Yonhap news agency reported.

The Anyang branch of Suwon District Court ordered the seizure of around 850 million won (US$725,000) worth of bonds the Japanese firm owns in LS Mtron, a South Korean industrial machinery manufacturer, according to the report.

The amount covers around 80 to 150 million won ordered to be provided to each of the victims and covers losses from the delay of payment.

"We request Mitsubishi to admit the historical fact and apologise and deliver compensation to the victims," Yonhap cited the law firm representing the plaintiffs as saying.

"If Mitsubishi continues to refuse to follow court orders, we will collect its bonds from LS Mtron based on the collection order," it added.

Japan says the victims' right to sue had been extinguished by the 1965 treaty which saw Seoul and Tokyo restore diplomatic ties and included a reparation package of about $800 million in grants and cheap loans.