TOKYO -- President Obama says he wants to visit Hiroshima and Nagasaki sometime during his presidency but won't have time during this week's trip to Japan to go to the cities devastated by U.S. atomic bombs at the end of World War II.

No sitting U.S. president has visited the two cities largely because of the controversy it could raise at home.

In an interview with Japanese broadcaster NHK that ran Tuesday, Obama said he would be unable to visit the cities on his trip to Japan this weekend due to time constraints but would be willing to do so in the future.

"The memories of Hiroshima and Nagasaki are etched in the minds of the world and I would be honored to have the opportunity to visit those cities at some point during my presidency," Obama said in the interview, done Monday at the White House.

Calls have grown in Japan for Obama to visit the two cities since his April speech in Prague envisioning a nuclear-free world and since he was named Nobel Peace Prize winner last month.

The mayors of Hiroshima and Nagasaki have invited Obama to their cities before a U.N. review of the Nuclear Nonproliferation Treaty next May. Japanese newspaper editorials and anti-nuclear activist groups have also called for Obama to come, pointing out that previous Nobel Peace Prize winners have visited the cities.

Many Japanese were impressed when new U.S. Ambassador John Roos visited Hiroshima last month, just weeks after he arrived in Tokyo.

A request by the Nihon Hidankyo, a nationwide organization for atomic bomb survivors, for a meeting with Obama was rejected because of the limited time he will be spending in Japan.

"We atomic bomb victims have been fighting for non-proliferation for the last 64 years," said 80-year-old Mikiso Iwasa, a leader of the group who became an orphan at 16 from the Hiroshima bombing on Aug. 6, 1945. It killed an estimated 140,000 people. The U.S. dropped a second bomb on Nagasaki on Aug. 9, killing 80,000. Six days later, Japan surrendered, ending the war.

"We hope that Obama will not take a step backward but achieve a world without nuclear weapons hand-in-hand with us," Iwasa said.

But traveling to either city could be a political minefield for any U.S. president. Signs of sympathy toward Japanese suffering could be seen as criticism of the decision to drop the bombs � viewed among many Americans as a pragmatic decision to hasten the end of the war that the U.S. entered after Japan attacked Pearl Harbor on Dec. 7, 1941.

Others see the bombings as crimes against humanity.

Former President Jimmy Carter stopped by the atomic bomb memorial in Hiroshima in 1984, after he was out of office. The highest-ranking American to visit while in office is House Speaker Nancy Pelosi, who went last year.

Obama is due to arrive in Tokyo on Friday to meet with Japanese Prime Minister Yukio Hatoyama before he flies on to an Asian summit in Singapore on Saturday.