At least two Washington-based lobby firms, Hogan Lovells and Hecht Spencer & Associates, are keeping tabs on the issue for the Japanese government, The Hill, a congressional newspaper, said in an article published online, Xinhua reported.
Citing Justice Department records, the paper said the government in Tokyo paid Hogan Lovells more than $523,000 from September 2012 to August 2013, while Hecht Spencer received $195,000 over the same period.
The Japanese government said it has repeatedly apologised over the treatment of women during Japan's occupation of Asia and Pacific islands in the 1930s and 40s, including a 1993 statement issued by then chief cabinet secretary Yohei Kono in which Japan acknowledged the military's responsibility for forced recruitment of women into sexual servitude and apologised to the victims.
"But past efforts in Japan to revise the statement, and remarks by some Japanese officials downplaying the issue, have inflamed activists and lawmakers," The Hill report said.
The US House of Representatives adopted resolution 121 in July 2007, urging the Japanese government to "formally acknowledge, apologise and accept historical responsibility in a clear and unequivocal manner" over the issue of "comfort women."
The US Congress included language in an omnibus spending bill last month that urged Secretary of State John Kerry to raise the issue with Japan.
"They (Japan) tried to stop it, but once it passed, they kept quiet. They tried to ignore the issue of comfort women," Chejin Park, a staff attorney for Korean American Civic Empowerment, was quoted as saying by The Hill.
"Every year, we have been asking them to do it... but they have never paid attention to the resolution," he added.
For Mike Honda, a Japanese-American congressman from California who introduced resolution 121, the issue "remains unresolved".
"There are those who believe the Japanese government has apologised and sufficiently addressed this issue. I vehemently disagree," Honda wrote in a letter sent Tuesday to Kerry.
He cited recent remarks by several Japanese public figures including the mayor of Osaka saying that comfort women were "necessary".
In his letter to Kerry, Honda noted that few of the survivors are still alive: 55 remain in South Korea, 26 in the Philippines, five in Taiwan, and a few others elsewhere in Asia and the Pacific.