 Media playback is unsupported on your device Media caption First known footage of 'comfort women' 
 
 South Korea has released what it says is the first known footage of "comfort women" forced to work as sex slaves for Japanese soldiers during World War Two. Image copyright US National Archives Image caption The issue has long been a strain on ties between South Korea and Japan 
 
 The research team says the footage was filmed by joint US-Chinese troops in China's Yunnan province which was previously occupied by Japan. The 18-second black-and-white clip shows seven women lined up outside a brick house, being questioned by Chinese soldiers. The term is used to describe girls and women from South Korea, China, the Philippines and elsewhere, who were forced into prostitution in Japanese wartime military brothels. South Korean activists estimate 200,000 women were forced into brothels for Japan's military. In 2015, the two countries reached a settlement whereby Tokyo formally apologised and agreed to pay 1bn yen ($8.3m, £5.6m) to fund victims. Many Koreans though viewed the apology as insufficient and the issue continues to plague ties. Japan wants South Korea to remove a statue near the Japanese consulate in Busan city commemorating Korean comfort women, as well as another near the Japanese embassy in Seoul, saying that the presence of the statues violates the 2015 agreement.
– It's just 18 seconds long, but a new video released by South Korean researchers makes history for the worst of reasons. The clip shows Korean "comfort women" held as sex slaves by the Japanese military, reports the BBC. It's believed to be the first such film clip known to exist, though images of "comfort women" had previously surfaced in still photographs. The good news is that the video shows the women after US and Chinese troops arrived to free them in China's Yunnan province in 1944. A research team from Seoul National University found the footage in the US National Archives after a two-year search, reports Reuters. An American soldier is believed to have filmed the scene, in which a Chinese officer talks to the women lined up in front of a building used as a brothel. Japan forced an estimated 200,000 women to work as sex slaves for its soldiers during World War II. (Earlier this year, South Korea angered Japan with a statue honoring the women.)