Emperor Naruhito said Wednesday he will mourn Japanese people who were detained by the former Soviet Union after World War II and died in Mongolia during his upcoming visit to the country.

"I want to pay tribute to those who died far from their homeland and think about their hardships," the emperor said at a news conference before departing with Empress Masako for Mongolia on Sunday.

Ahead of the 80th anniversary of the end of the war in August, the emperor and empress earlier this year visited Okinawa and Hiroshima prefectures, and Iwoto — also known as Iwo Jima.

The emperor said the "suffering and sorrow" experienced by people in these places "should never be forgotten."

Through meetings with people who survived the war during the visits, the emperor said, "I was deeply pained when I caught a glimpse of the unimaginable hardships, and renewed my belief in the importance of peace." He stressed that it is "extremely important" to pass on memories of the war to younger generations.

Emperor Naruhito also said it was "very heartbreaking" that many lives were lost around the world during the war. "It's important to remember those who died, deepen understanding of past history, and foster a peace-loving heart," he noted.

The emperor last visited Mongolia in 2007, when he was crown prince. "I hope to see how (Mongolia) has changed," he said, adding that his upcoming visit "will hopefully be an opportunity to further strengthen our countries' close friendship."

Empress Masako "is looking forward to interacting with people in Mongolia and experiencing the great nature, history and culture of Mongolia," the emperor said.