UNESCO, however, recommended the nomination of "Joseon Tongsinsa," which consists of old diplomatic records of Korean envoys to Japan, a royal seal and an investiture book collection of the Joseon Dynasty, as well as archives of the National Debt Redemption movement from 1907 to 1910.

South Korea so far has 16 historical items recognized by UNESCO's Memory of the World initiative.

The IAC comprised of private-sector experts makes recommendations to the chief of UNESCO, who has the final say.

Though it has not been officially involved, the Seoul government has supported the civic group-led push for the listing, saying that lessons should be learned from the dark history and that efforts should also be made to let future generations know more accurately about historical facts.

South Korea expressed regret over the UNESCO decision.

"The government expresses our regret over the IAC's recommendation and the decision by its secretary general," the foreign ministry said. "We oppose any remarks or actions that run counter to the historical truth related to the victims... We will continue possible diplomatic efforts to make the records on comfort women objectively and fairly evaluated going forward."

The Japanese, in particular, have protested to the South Korean government that pushing for a UNESCO listing of such documents might run counter to the spirit of a controversial deal reached between the two countries to address grievances on wartime atrocities committed by Japan.

In December 2015, the two reached the deal under which they agreed to "finally and irreversibly" resolve the comfort women issue. Tokyo gave an apology for its colonial-era atrocities and agreed to contribute 1 billion yen ($8.9 million) to a foundation dedicated to supporting the victims.

Historians say more than 200,000 women, mostly Koreans, were coerced into sexual servitude in front-line Japanese brothels during World War II, when the Korean Peninsula was a Japanese colony. (Yonhap)