U.S. President Barack Obama said North Korea poses the "biggest challenge" to efforts to realize a world without nuclear weapons.

Obama made the remark in an interview with Japan's NHK television, saying one of the purposes of his planned visit to the Japanese city of Hiroshima is to demonstrate his commitment to a nuclear-free world.

"I think the biggest challenge we have right now with respect to nuclear weapons is the dangers of the nuclear program in Pyongyang, in North Korea. And there has been, I think, a continued effort on their part not only to develop nuclear weapons, but also deliver them in ways that are reckless and provocative," Obama said.

"The international community has shunned them for their behavior, but so far they haven't changed their behavior the way they need to," he said.

Pyongyang's record of nuclear proliferation is also a cause for concern, Obama said.

"North Korea is the worst example but we also have other parts of the world where you'll still see the development of new nuclear technologies that could be very dangerous," he said.

Obama said that resources for nuclear development should be diverted into such areas as food, health care and education.

Obama will be the first sitting U.S. president to visit Hiroshima since the U.S. dropped an atomic bomb there at the end of World War II. White House officials said Obama will use the visit to highlight his commitment to a world without nuclear weapons and to honor the memory of all innocents who were lost during the war.

The planned visit, however, raised concern that it could dilute Japan's wartime aggression by making the country look like a victim, even though U.S. officials said the visit shouldn't be interpreted as an apology and Obama won't revisit the decision to use the atomic bomb.

When asked during the interview if he's going to offer an apology, Obama flatly said, "No."

"I think that it's important to recognize that in the midst of war, leaders make all kinds of decisions. It's the job of historians to ask questions and examine them," he said.

Instead, Obama said he will emphasize "how we can move forward."

"My purpose is not to simply revisit the past, but to affirm that innocent people die in a war, on all sides, that we should do everything we can to try to promote peace and dialogue around the world, that we should continue to strive for a world without nuclear weapons. That is something that I worked on since I first came into office," he said. (Yonhap)