Seoul: South Korea intends to build a museum in memory of wartime sex slaves for Japanese troops, a government minister said on Monday, re-igniting a perennial diplomatic thorn in the two neighbours’ sides.

The plight of the so-called ‘comfort women’ who were forced into sexual slavery for Japanese troops during World War II is a hugely emotional issue that has marred ties between the US allies for decades.

Mainstream historians say up to 200,000 women — mostly from Korea but also other parts of Asia including China — were forced to work at Japanese army brothels across the region during the 1939-1945 conflict.

‘We are planning to build a ‘comfort women’ museum in Seoul,’ said new gender equality minister Chung Hyun-Back at a shelter for a shrinking number of survivors, who now number only 38 in total.

The ‘House of Sharing’, in a rural area south of Seoul, has a memorial hall but Chung said the country needed a museum in the capital with better public access.

She did not elaborate on when it will open or what kind of materials it will display.

Japan maintains that there is a lack of documentary proof that the women were forcibly made to work at the brothels.

In late 2015, under now-ousted president Park Geun-Hye, Seoul and Tokyo reached what they described as a ‘final and irreversible’ agreement under which Japan offered an apology and a one-billion yen ($8.6 billion) payment to South Korean survivors.

Critics of the accord, including some survivors, say the deal did not go far enough in holding Japan legally responsible for wartime abuses during its 1910-45 colonial rule over the Korean peninsula.

Tension escalated further after South Korean activists refused to remove a statue of a girl erected in front of the Japanese embassy in Seoul to symbolise the victims of sex slavery.

Tokyo has pressed Seoul to remove it, but activists have since put up more statues — including one outside the Japanese consulate in Busan.

Tokyo recalled its ambassador in protest in January, and he did not return for three months.

New South Korean President Moon Jae-In has repeatedly voiced criticism of the 2015 deal, suggesting a potential push by Seoul to renegotiate it. 

Monday’s comments came after South Korean researchers last week unearthed what they described as rare footage of the sex slaves during the war.

The 18 seconds of film, discovered at the US national archive and believed to be taken in 1944, shows a group of seven women standing in front of a hotel used as a Japanese military brothel in Songshan, China.

They were not named, but some of them were identified as the same women featured in another rare photo showing Korean comfort women, according to researchers at the Seoul National University.