US lawmakers have called on Japan's government to formally apologise for its role in forcing thousands of women to work as sex slaves in World War II.

The symbolic and non-binding resolution was passed during a voice vote in the House of Representatives.

Up to 200,000 "comfort women" were part of Japan's wartime military brothel programme that started in the 1930s.

Japan says it has shown sufficient remorse over the issue, but survivors and relatives say it should go further.