The Japanese government has stirred further controversy by again saying it had found no evidence that Asian women were forced to be wartime sex slaves.
Many ex-comfort women are angry at Japan's position on the issue
The statement was made in response to a question from an opposition lawmaker.
PM Shinzo Abe sparked anger overseas earlier this month when he said there was no evidence women were "coerced" into World War II military brothels.
The US ambassador to Japan has disputed Mr Abe's comments, saying there appears to be clear evidence of coercion.
Thomas Schieffer said he took the word of three women who recently told the US Congress of their experiences being kidnapped by Japanese troops and turned into sexual slaves.
"I think they were coerced, that means they were raped by the Japanese military," he said. "I think the events speak for themselves."
Mr Schieffer said he hoped Tokyo would continue to stand by a 1993 apology, which acknowledged that the military set up and ran brothels for its troops during the war.
Some conservatives want the apology to be softened, arguing that the women were professional prostitutes who were paid for their services and that private contractors rather than the military were responsible for any abuses.
Many historians say Japan compelled up to 200,000 women - many of them from China and Korea as well as the Philippines, Indonesia and Taiwan - to become sex slaves during the war.
Unequivocal apology sought
The Japanese government statement said it "had not come across anything recorded in the materials it has found that directly shows so-called "coercion" on the part of the military or constituted authorities".
The statement was made as a result of a query by opposition lawmaker Kiyomi Tsujimoto.
Mr Abe says he stands by the 1993 apology
Earlier this month, Mr Abe made similar comments, telling reporters "there was no evidence to prove there was coercion as initially suggested".
He was speaking in response to a non-binding resolution before the US House of Representatives which calls for Tokyo to make an unequivocal apology over the army's use of so-called comfort women.
Mr Abe's remarks drew sharp criticism from China and South Korea in particular.
However, the Japanese prime minister has said he continues to stand by the 1993 apology, which was made by the then Chief Cabinet Secretary Yohei Kono.