SADO, Niigata (AP) -- Japan is holding a memorial ceremony on Sunday near the Sado Island Gold Mines, which were listed this summer as a UNESCO World Heritage site after the country settled years of historical disputes with South Korea and reluctantly acknowledged the mines' dark history.

At these mines, hundreds of Koreans were forced to labor under abusive and brutal conditions during World War II, historians say. The Japanese government says Sunday's ceremony will pay tribute to "all workers" who died at the mines, but without spelling out who they are -- part of what critics call a persistent policy of whitewashing Japan's history of sexual and labor exploitation before and during the war.

Ahead of the ceremony Sunday, The Associated Press explains the Sado mines, their history and the controversy.

What are the Sado gold mines?

The 16th century mines on the island of Sado, about the size of the Pacific island of Guam, off the western coast of Niigata prefecture, operated for nearly 400 years beginning in 1601 and were once the world's largest gold producer. They closed in 1989. During the Edo period, from 1600 to 1868, the mines supplied gold currency to the ruling Tokugawa Shogunate.

Today, the site has been developed as a tourist facility and hiking site where visitors can learn about the changes in mining technology and production methods while looking at the remains of mine shafts and ore dressing facilities.

Critics say the Japanese government only highlights the glory of the mines and covers up its use of Korean victims of forced labor and their ordeals. The mines were registered as a cultural heritage site in July after Japan agreed to include an exhibit on the conditions of Korean forced laborers and to hold a memorial service after repeated protests from the South Korean government.

What's the controversy?

At the July meeting of the UNESCO World Heritage Committee, the Japanese delegate said Tokyo had installed new exhibition material to explain the "severe conditions of (the Korean laborers') work and to remember their hardship."

Japan also acknowledged that Koreans were made to do more dangerous tasks in the mine shaft, which caused some to die. Those who survived also developed lung diseases and other health problems. Many of them were given meager food rations and nearly no days off and were caught by police if they escaped, historians say. But the Japanese government has refused to admit they were "forced labor."

South Korea had earlier opposed the listing of the site for UNESCO World Heritage on the grounds that the Korean forced laborers used at the mines were missing from the exhibition. South Korea eventually supported the listing after consultations with Japan and Tokyo's pledge to improve the historical background in the exhibit and to hold a memorial that also includes Koreans.

Historians say Japan used hundreds of thousands of Korean laborers, including those forcibly brought from the Korean Peninsula, at Japanese mines and factories to make up for labor shortages because most working-age Japanese men had been sent to battlefronts across Asia and the Pacific. About 1,500 Koreans were forced to work at the Sado mines, according to Yasuto Takeuchi, an expert on Japan's wartime history, citing wartime Japanese documents.

The South Korean government has said it expects Japan to keep its pledge to be truthful to history and to show both sides of the Sado mines.

"The controversy surrounding the Sado mines exhibit underscores a deeper problem" of Japan's failure to face up to its wartime responsibility and its growing "denialism" of its wartime atrocities, Takeuchi said.

Who does the ceremony commemorate?

All workers who died at the Sado mines will be honored. That includes hundreds of Korean laborers who worked there during Japan's 1910-1945 colonization of the Korean Peninsula.

Officials say the ceremony is organized by a group of local Japanese politicians, business owners and other volunteers who campaigned for the Sado mines to win the UNESCO status, but preparations were handled by local government officials, who did not disclose details, including guests and programs, until the last minute.

Foreign Minister Takeshi Iwaya announced the ceremony on Friday, but he declined to comment on "diplomatic exchanges."

Officials at Sado city and the Foreign Ministry said about 100 people, including officials from Japan's local and central government, as well as South Korean Foreign Ministry officials and the relatives of Korean wartime laborers, have been invited. Attendants are expected to observe a moment of silence for the victims who died at the mines due to accidents and other causes.

The ceremony dredged up long-standing frustrations in South Korea.

South Korea's Foreign Ministry has been accused of lacking transparency over the way it handled the communication with Tokyo as critics question why Seoul was throwing its support behind an event without securing a clear Japanese commitment to highlight the plight of Korean forced laborers.

During its weekly briefings, the ministry has refused to elaborate on the details or its discussions with Japanese counterparts or why the South has agreed to pay for the travel expenses of the Korean victims' family members who were invited to attend the ceremony.

How has Japan faced up to its wartime atrocities?

Critics say Japan's government has long been reluctant to discuss wartime atrocities. That includes what historians describe as the sexual abuse and enslavement of women across Asia, many of them Koreans who were deceived into providing sex to Japanese soldiers at frontline brothels and euphemistically called "comfort women," and the Koreans who were mobilized and forced to work in Japan, especially in the final years of World War II.

Korean compensation demands for Japanese atrocities during its brutal colonial rule have strained relations between the two Asian neighbors, most recently after a 2018 South Korean Supreme Court ruling ordered Japanese companies to pay damages over their wartime forced labor.

Japan's government has maintained that all wartime compensation issues between the two countries were resolved under the 1965 normalization treaty. Ties between Tokyo and Seoul have improved recently after Washington said their disputes over the historical issues were hampering crucial security cooperation as China's threat grows in the region.

Japan's whitewashing of wartime atrocities has risen since the 2010s, particularly under the past government of revisionist leader Shinzo Abe. For instance, Japan says the terms "sex slavery" and "forced labor" are inaccurate and insists on the use of highly euphemistic terms such as "comfort women" and "civilian workers" instead.

South Korea's conservative President Yoon Suk Yeol announced in March 2023 that his country would use a local corporate fund to compensate forced labor victims without demanding Japanese contributions. Japan's then-Prime Minister Fumio Kishida later expressed sympathy for their suffering during a Seoul visit. Security, business and other ties between the sides have since rapidly resumed.

Takeuchi said listing Japan's modern industrial historical sites as a UNESCO World Heritage is a government push to increase tourism. The government, he said, wants "to commercialize sites like the Sado mines by beautifying and justifying their history for Japan's convenience."