The government said Thursday it has documents showing Allied POWs worked at a coal mine run by Prime Minister Taro Aso's family during World War II.

Many similar documents have surfaced, but this is the first time the government has acknowledged that Aso Mining Co. in Fukuoka Prefecture used POWs, said Yukihisa Fujita of the Democratic Party of Japan.

"Prisoner policy is important in many ways for diplomacy, and it is a major problem that the issue has been neglected for so long," Fujita said at a news conference. "For a long time, the government has been continuing to deny the many revealed documents and the (existence of) POWs" at Aso Mining.

Although the use of POWS as laborers was not illegal in Japan during the war, their maltreatment violates the Geneva Conventions, which Japan was not party to, and the government has been reluctant to delve into the history of Aso Mining.

Fujita, who requested the probe, said the key point to the Aso Mining issue is whether the POWs were mistreated by the company.

At a meeting of the Upper House panel on foreign affairs and defense Thursday, an unnamed health ministry bureaucrat revealed that Aso Mining had used 300 Allied POWs between May 10 and Aug. 15, 1945.

Of the 300, 101 were Britons, two were Dutch and 197 were Australians. The bureaucrat also announced that two of the Australians died while working there, although their names and causes of death were not disclosed for privacy reasons.

The government also acknowledged that a report on POW treatment that Aso Mining submitted to the Japan POW Investigation Section in 1946 was authentic. The report, stored at the U.S. National Archives and Records Administration, was submitted to the panel by Fujita last month.