Updated

The South Korean government on Thursday released rare video that shows Korean women—known as “comfort women”-- who were forced to work in brothels for the Japanese military during WWII.

The 1944 video, which was filmed by an American soldier, is a black-and-white clip that lasts 18 seconds, Reuters reported. The women are lined up outside a brick house. The report, citing research from Seoul National University, said the women were found by U.S.-China allied forces in Yunnan province, in China.

Many Korean and other women in Asia were forced into sexual slavery in front-line brothels for the Japanese military during World War II in what was called the “comfort woman” system. The precise number is unclear. Some estimates put the number at 200,000.

FLOODS IN SOUTHERN JAPAN TURN DEADLY

“Comfort women” were used by the Japanese military for sex and were present wherever the army invaded and occupied Asia countries from the early 1930s through the end of the war.

The topic has long been the source of tension between the Japanese and South Koreans. Earlier this year, Japan announced it would recall its ambassador to South Korea and suspend economic talks in response to the placing of a “comfort woman” statue in the Korean port city of Busan.

The Associated Press contributed to this report.