The U.S. Defense Department document, "Transfer of U.S. Korean War POWs to the Soviet Union," and dated Aug. 26, 1993, said that North Korea sent South Korean and U.S. soldiers to a secret program in the Soviet Union approved by top Soviet leaders. The document was obtained by Seoul's Yonhap news agency.

Six months after the North invaded the South in June 1950, the North's state-run Radio Pyongyang trumpeted reports that the North Korean army had captured more than 65,000 South Koreans as prisoners of war. But it repatriated only 7,142 after the signing of the Korean Armistice in July 1953.

Seoul's Defense Ministry says some 19,000 South Korean soldiers are listed as missing in action. The ministry estimates that a total of 1,186 South Korean POWs were held in the North and that 542 of them are still stranded there.

The POWs were sent to remote regions to exploit and counter U.S. aircraft technologies. The document said the POWs were never repatriated and were used as human shields and for general intelligence purposes.

Kang San-Kho, a former North Korean official who later settled in the Soviet Union, testified in 1992 that he had assisted North Korea in sending thousands of prisoners to 300 to 400 military camps across the Soviet Union and Central Asia, according to the document. Kang died at 91 in 2000 in Saint Petersburg.

The document also said in September 1952 Joseph Stalin and Chinese Foreign Minister Zhou Enlai discussed keeping 20 percent of the POWs as hostages.

"Prisoners were moved by various modes of transportation. Large shipments moved through Manchouli and Pos'yet," the document was quoted as saying. Khabarovsk was the hub of a major interrogation operation of UN POWs from South Korea, it said.

South Korea's Defense Ministry questioned the document's authenticity and said it would ask the United States to review it.