South Korean President Moon Jae-in has said Japan has no right to claim the issue of "comfort women" is settled since the country was the colonial master overseeing the sex slavery of Korean women.

Repeating his calls for Japan to apologise over its colonial past, Moon reiterated the 2015 comfort women deal signed between Seoul and Tokyo under South Korea's previous administration was deeply flawed.

"Also in resolving the issue of sexual slaves, the Japanese government, the perpetrator, must not say it is "over'," said the South Korean president as he was addressing the anniversary of what is known as the March 1 Movement. Tens of thousands of South Koreans marked the event across the country to commemorate the end of Japan's rule.

"The issue of a crime against humanity committed in time of war cannot be closed with just a word. A genuine resolution of unfortunate history is to remember it and learn a lesson from it," added Moon.

The South Korean president went on, "Inhumane violation of human rights during the war cannot be covered by saying it is over. A true resolution only comes from remembering history and learning from that history, especially when it is the history of an unfortunate past."

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.

Moon continued: "I wish Japan will truly make up with the neighbouring countries it oppressed and together walk the path of peaceful co-prosperity. I do not demand special treatment from Japan. I simply want Japan to move into the future with us based on its sincere reflection and apology."

For decades, the two neighbours, both close allies of the US, have been locked in strained relations due to the "comfort women" matter. Japan was quick to express regret over Moon's remarks and asked the South to honour the 2015 agreement. Tokyo is also expected to register its protest via diplomatic channels.

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.

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.

Comfort women
The sexually enslaved Korean women by the 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