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 vote in the House of Representatives.
Up to 200,000 "comfort women" from across the Far East were part of Japan's military brothel programme.
Japan says it has shown sufficient remorse over the issue. A spokesman said the resolution was "regrettable".
Chief Cabinet Spokesman Yasuhisa Shiozaki told a news conference that Japan had "handled the comfort women issue with sincerity".
Prime Minister Shinzo Abe had "clearly explained his views" on the subject during a visit to Washington in April, he said.
The resolution calls on Japan - one of the strongest US allies in Asia - to "formally acknowledge, apologise and accept historical responsibility in a clear and unequivocal manner" for the suffering of the women.
"Those who posit that all of the comfort women were happily complicit and acting of their own accord simply do not understand the meaning of the word rape"--Tom Lantos, House Committee on Foreign Affairs chairmanEarlier this month, a group of Japanese lawmakers demanded the US government retract the resolution, saying it was based on "wrong information that is totally different from the historical fact".
Tom Lantos, chairman of the House of Representatives Committee on Foreign Affairs, described attempts to deny the use of sex slaves as "nauseating".
"There can be no denying the Japanese imperial military coerced thousands upon thousands of Asian women," Mr Lantos said.
"Those who posit that all of the comfort women were happily complicit and acting of their own accord simply do not understand the meaning of the word rape."
In 1993 Japan issued an official apology for the suffering of comfort women, acknowledging its involvement managing the brothels. But it was never approved by parliament and Japan has rejected most compensation claims, saying they were settled by treaties.
Mr Abe caused an uproar in March when he said there was no proof that the government or the military had forced the women into sexual servitude.
He later apologised, saying he felt sympathy for those affected.
The resolution comes at a difficult time for Mr Abe. On Sunday his ruling coalition suffered a crushing defeat in upper house polls, losing its majority and handing control of the house to the opposition.
He is facing pressure from the public and the media to step down, but the premier says he plans to remain in office and continue with an agenda of reform.