Japan has acknowledged that it conducted only a limited investigation before claiming there was no official evidence that its imperial troops coerced women into sexual slavery before and during World War II.
A parliamentary statement signed by Prime Minister Shinzo Abe on Tuesday acknowledged the government had a set of documents produced by a postwar international military tribunal containing testimony by Japanese soldiers about abducting Chinese women as military sex slaves.
That evidence apparently was not included in Japan's only investigation of the issue, in 1991-1993.
Tuesday's parliamentary statement also said documents showing forcible sex slavery may still exist. The statement did not say whether the government plans to consider the documents as evidence showing that troops had coerced women into sexual slavery.
Abe has acknowledged so-called "comfort women" existed but denied they were coerced into prostitution, citing a lack of official evidence.
He also has repeatedly vowed to reassess apologies by past Japanese administrations.
The parliamentary statement, released on Tuesday and seen by the Associated Press on Wednesday, comes in response to an official inquiry last month to the upper house of Parliament by opposition lawmaker Tomoko Kami, who said the government's investigation into sex slavery was "insufficient" and documents it claimed to have collected were incomplete.
Kami, of the Japan Communist Party, also asked whether the government had ever updated its archives to reflect more recent findings than the earlier investigation to which the answer was no.
Over the past two days, top officials of Abe's conservative government have appeared to soften their stance on Japan's past apologies to neighbouring countries for wartime atrocities committed by the Imperial Army, saying Japan does not plan to revise them.
The backtracking appears intended to allay criticisms of Abe's earlier vows to revise the apologies, including an acknowledgement of sexual slavery during the war, and to calm tensions with neighbours South Korea and China.
The US government has also raised concerns about Abe's nationalist agenda.
The statement acknowledged documents produced by the 1946-1948 International Military Tribunal for the Far East, held in Tokyo, but said they were not in the Cabinet Secretariat's archives.
It did not say when the documents were found or whether they are reflected in any official statements about sexual slavery.