The topic of "comfort women" — those women who were forced to work as sex slaves during the Second World War — is so sensitive in Japan and South Korea that it still invokes pain and anger more than half a century later.

More than 200,000 women — often euphemistically referred to as "comfort women" — from Korea, Taiwan, China and other nationalities were forced to work at wartime brothels by the Japanese Imperial Military during the Second World War. It was one of the biggest human trafficking cases of the 20th century.

While some of the enslaved women were thought to be as young as 12, a vast majority of the victims were under 20.

The severity of their psychological trauma emerged only in the 1990s when several victims began speaking out about their ordeal. Most of the surviving victims have been campaigning against better recognition of the atrocities committed during Japan's bloody colonial rule.

Several decades after the 1910-1945 Japanese occupation of the Korean peninsula, the issue continues to remain a highly delicate and complex matter in both Japan and South Korea.

The two countries had signed a crucial deal to close the issue in 2015. However, discontent has surfaced two years after the agreement with demands for renegotiating the terms, which has put considerable strain on the two American allies who are united on their stand against North Korea.

However, the two countries are unlikely to have a full-blown diplomatic tussle over the issue of "comfort women" as the threat looming from their common adversary, North Korea, is larger. But political and diplomatic frictions over such sensitive issues are always a cause for serious concern.

Successive administrations in the US have also urged the two countries for a better cooperation during the past years against the backdrop of China's increasing assertions in the region compounded by the North Korean threats.

When signed, the deal came under strong criticism in South Korea because it was believed the Park Geun-hye government had agreed to too little.

As part of the 2015 accord, Japan had apologised to the victims and pledged 1bn yen ($8.8m, £6.1m) termed carefully as a humanitarian offer and not reparation – to the dwindling number of survivors.

But, South Korean President Moon Jae-in, who had pledged to normalise relations with Tokyo, said on Thursday, 28 December, that the specifics of the bilateral agreement was flawed. Japan, on the other hand, has made it clear the deal will not be altered.

Moon, a liberal who pledged to rearrange the deal in his presidential campaign, set up a panel to examine the agreement and following its findings, has now demanded that it be reworked. The South Korean government, however, stopped short of calling the arrangement null.

"It has been confirmed that the 2015 comfort women negotiation between South Korea had serious flaws, both in process and content," said Moon. "Despite the burden of the past agreement being a formal promise between governments that was ratified by the leaders of both countries, I, as President and with the Korean people, once again firmly state that this agreement does not resolve the issue over comfort women."

Comfort women
The Korean women enslaved by Japanese soldiers in Yunnan province, located in China's southwest, were filmed by an American soldier after the US-China allied forces captured the area from the Japanese military during World War II Seoul National University Human Rights Center/Seoul Metropolitan Government