A court in South Korea has begun the hearing of a long-awaited civil case filed against the Japanese government by South Korean women who were forced to work in Japan‘s World War II military brothels.

The trial on Wednesday at the Seoul Central District Court proceeded with empty seats in the defendant’s dock because Japan has refused to participate in the case, saying its sovereign immunity shields it from lawsuits in other countries, according to court officials and the plaintiffs’ lawyers.

A group of 20 former sex slaves and relatives filed the suit in 2016 seeking compensation of $171,000 each, but the process was delayed after the Japanese government refused to receive copies of the complaint.

Japan insists that all compensation matters were settled by a 1965 treaty that normalised relations between the countries and has accused South Korea of repeatedly opening the book on issues that were supposed to be settled.

The case comes amid a deep dispute between Seoul and Tokyo over wartime history, triggered by a ruling by South Korea’s Supreme Court last year that called for Japanese companies to offer reparations to ageing South Korean plaintiffs for their World War II forced labour.

The dispute escalated into a trade war that saw both countries downgrade the other’s trade status, and then spilled over to military matters when Seoul threatened to end a 2016 military intelligence-sharing agreement with Tokyo.

Former South Korean ‘comfort woman’ Lee Ok-seon, centre, leaves the Seoul Central District Court in Seoul, South Korea [Ahn Young-joon/AP]

“The Japanese government must repent,” Lee Ok-seon, a former sex slave, said at a news conference shortly before the trial began. “They kidnapped innocent kids and inflicted irreversible damages and they must repent. They must sincerely apologise.”

It is not immediately clear how long the case will take. The court will rely solely on the plaintiffs’ legal arguments before making a verdict.

In an opinion submitted to the court on Tuesday, Amnesty International said a statute of limitations and Japan’s sovereign immunity should not be applicable to serious human rights violations and war crimes like military sexual slavery. The group also cited the South Korean Supreme Court ruling on forced labourers that said the 1965 treaty does not block individual claims for reparations.

Under South Korea’s previous conservative government, the countries attempted to settle their decades-long dispute over sexual slavery in 2015 when they reached an agreement for Tokyo to fund $9m to a Seoul-based foundation to help support victims.

The deal was hugely unpopular in South Korea, where many people criticised their government for settling for far too less and accused Tokyo of attempting to silence the victims with money. The government of South Korean President Moon Jae-in, who took office in 2017, took steps to dissolve the foundation, saying the deal lacked legitimacy because officials failed to properly communicate with victims before reaching it.

About 240 South Korean women came forward and registered with the government as victims of sexual slavery by Japan’s wartime military, but only 20 are still alive.