TOKYO — Japan’s Emperor Naruhito began a weeklong visit to Mongolia on Sunday during which he plans to honor thousands of Japanese prisoners of World War II who were held under harsh conditions in the country.

Naruhito’s visit marks the 80th anniversary of the end of WWII. In recent years, he has toured some of the places where the bloodiest battles and bombings occurred, including Iwo Jima, Okinawa and Hiroshima. The emperor has said it’s part of his effort at atonement and remembrance of the tragedy of war fought in the name of his grandfather, Emperor Hirohito.

While the vast majority of Japanese soldiers were taken to Siberia, around 12,000 to 14,000 ended up in Mongolia, which was fighting alongside the Soviets against Japan.

Most of the POWs were put to hard labor and construction work for the Mongolian government’s headquarters, a state university and a theater that are still preserved in the capital Ulaanbaatar. The prisoners toiled under harsh conditions and scarce food. Japanese records show about 1,700 of them died in Mongolia.

“As we mark the 80th anniversary of the end of the war this year, we should never forget the pain and sorrow of the people,” Naruhito said last week. “I believe it is important to not forget those who died, deepen understanding of the wartime past and to nurture the peace-loving heart.”

Naruhito and Masako were scheduled to meet Mongolia’s President Ukhnaa Khurelsukh and his wife. The couple will also attend the opening ceremony of Naadam, Mongolia’s annual festival that focuses on three traditional games of horseracing, wrestling and archery.

Naruhito had previously visited Mongolia as crown prince in 2007.

Associated Press writer Mari Yamaguchi contributed to this report.