OSAKA – San Francisco formally adopted a resolution Tuesday calling for the city to build a memorial to commemorate the “comfort women” who were forced to provide sex at Japanese military brothels before and during World War II.

The memorial has been hailed by supporters as an important step in educating local residents about past — and current — human-rights abuses against women, including domestic violence and human trafficking. However, it’s likely to further complicate relations with Osaka, San Francisco’s sister city, where Mayor Toru Hashimoto has been staunchly opposed to the memorial.

In a unanimous vote, the 11-member Board of Supervisors passed the resolution to build the memorial on public land to remember what it says were an estimated 200,000 women and young girls forced into sexual slavery by the Japanese Imperial Army during its colonial and wartime occupation of Asia and the Pacific islands.

“Let’s send a clear message of justice, of compassion, and of unity in saying ‘never again,’ ” said Supervisor Eric Mar, the legislation’s key sponsor. “The resolution is the first step toward education about the issue.”

The city has not yet approved a budget for the memorial, although Mar said over $140,000 had already been raised through private donations. Over the coming months, he added, community leaders will discuss potential locations and designs.

The resolution was approved despite concerns among some in the local Japanese-American community that it could lead to a backlash. In Japan, opponents wrote to the various supervisors, urging them to vote the measure down.

In early September, Hashimoto, who was officially condemned by the San Francisco Board of Supervisors over 2013 remarks that the comfort women system had been necessary at the time, sent a letter to the board expressing his opposition to the measure.

In it, he voiced support for the dignity and human rights of all women, but said a comfort women monument focusing only on what Japan did during the war period was unfair.

Hashimoto also disputed the figure of 200,000 women and girls alleged to have been forced into sexual slavery, adding that he was concerned this figure would end up being engraved on the San Francisco memorial. A comfort women memorial in Glendale, California, also bears this number.

Phyllis Kim, executive director of the Korean American Forum of California and a key backer of the resolution, said that Hashimoto’s letter twisted the facts.

“Sexual slavery by the Japanese Imperial Armed Forces from 1932 until 1945 was the largest known crime against humanity of its kind,” she said. “Hashimoto’s argument that the issue should be considered as equal with all other sexual crimes during wartime doesn’t hold much water because it truly is the largest case of systematic enslavement of women for sexual purposes, thus a crime against humanity organized by a government.”

Earlier this year, a group of prominent historians and Asian scholars based mainly in the U.S. and Europe sent a letter of support to Japanese historians, some of whom have faced a backlash from right-wing academics, politicians and media that have long insisted the Japanese government and military was not directly involved in recruiting the women and did not force them to serve in comfort women stations.

The hundreds of scholars who have since signed the letter noted that while a lack of documentation has prompted disagreement over the precise number of comfort women, Japan’s system was distinguished from that of other countries by its large scale and systematic management under the military.

Although the letter did not mention figures, estimates of the number of comfort women vary between 20,000 and 200,000.