The city of Osaka, Japan, has ended its "sister city" ties with San Francisco over the display of a statue depicting women forced to work as sex slaves for Japanese soldiers during World War II.

The memorial, entitled the "Women's Column of Strength", consists of three women made of bronze. They are holding hands in a circle with their backs to each other as they look into the distance.

The statue to the side depicts Kim Hak-sun, the woman first to break her silence about her experience as a "comfort woman".

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The women depicted represent women from Korea, China and the Philippines - the countries the 'comfort women' were from.

The statue was initially unveiled in September 2017 but officially accepted by the US City in November. It was launched at a time when much of the country debated pulling down controversial statues.

It was also launched despite efforts by the Japanese government to halt the erection of the statue.

In turn, Osaka mayor Hirofumi Yoshimura announced the end of Osaka's 60-year sisterhood with San Francisco in November.

But the move was delayed following the death of San Francisco Mayor Ed Lee in December.

In a letter to the current Mayor London Breed, Mr Yoshimura declared he had issues with the monument's inscription, which he said "presents uncertain and one-sided claims as historical facts".

"There is also disagreement among historians when regarding the historical facts such as the number of 'comfort women', the degree to which the former Japanese army was involved, and the extent of the wartime harm", his letter adds.

Ms Breed wrote in a statement that one mayor could not unilaterally end a relationship that had existed since 1957.

She described the memorial as "a symbol of the struggle faced by all women who have been, and are currently, forced to endure the horrors of enslavement and sex trafficking."

"These victims deserve our respect and this memorial reminds us all of events and lessons we must never forget," she added.

A hurtful symbol

Amnesty International says up to 200,000 women were forced to work in Japanese military brothels during World War II, often through coercion and deception.

Japan apologised in 1993 but the issue has remained an open rift with its neighbours, particularly South Korea, which was under Japanese colonial rule from 1910 and 1945.

South Korean activists, including former comfort women, have accused Japan of playing down the atrocity, and an organization in San Francisco has taken up their cause. But Japanese officials say that criticism is one-sided and an obstacle to reconciliation.

The United Nations has been critical of Japan not doing enough to support the victims.

'Comfort women' in Australia

A similar statue was erected in the Sydney suburb of Ashfield in 2016, at the local Uniting Church.

The Australia-Japan Community Network lodged a complaint under section 18C of the federal racial discrimination act against the memorial, suggesting the statue promoted animosity.

But the Human Rights Commission said the complaint had been thrown out on the grounds that it was “misconceived and/or lacking in substance”.

A spokeswoman for the Ashfield Uniting Church confirmed to SBS News that the statue continues to stand on the Church's ground to this day.