It has previously been estimated that there were between 50,000 and 200,000 trøstekvinder during the Second world War.

The imperial japanese army asked the government to provide one so-called trøstekvinde for each 70. soldier during the Second world War.

It writes the japanese news agency Kyodo News, which has reviewed a number of documents.

they include The concealed letters sent from japanese consulates in China to the foreign ministry in Tokyo dating back to 1938.

The japanese military's use of sex slaves, the so-called trøstekvinder, has long been a point of contention between Japan and south Korea.

Many of the women, who were forced to be prostitutes in the japanese military brothels were Korean.

In a letter from the consulate general in the chinese port city of Qingdao to become the ministry asked to send a woman for every 70. soldier.

In a second letter from the Shandong-province, please, that "at least 500 trøstekvinder to be assembled here", while the japanese forces move forward.

You have several times tried to put the sentence in the dispute between Japan and south Korea.

"Kono-opinion" from 1993 was the japanese authorities ' involvement in coercing the women to work in brothels recognized.

And in 2015, admitted the japanese government and the then minister for foreign affairs, that he felt "a deep responsibility" for the women's fate. At the same time, gave millions to a fund to help the victims.

But there are still disagreements on what degree the japanese government has been involved.

- recent documents (...) has given us detailed information about how the brothels were operated, and where many of the soldiers, which was awarded a so-called trøstekvinde, said Yoon Mi-hyang, head of an organization for the victims of japanese sexual slavery.

- This is a clear sign that the japanese government is responsible for deliberately recruit Korean women for sexual slavery.

There was no immediate comment from the government in Japan, which are to collect the official documents on the trøstekvinder.

/ritzau/Reuters