U.S. Republican presidential candidate Donald Trump has faulted President Barack Obama over his recent visit to the atomic-bombed Japanese city of Hiroshima, saying he didn't even mention Japan's bombing of Pearl Harbor.

"Does President Obama ever discuss the sneak attack on Pearl Harbor while he's in Japan? Thousands of American lives lost," Trump said of Obama's visit to the Hiroshima Peace Memorial in a Twitter message Saturday ahead of Monday's Memorial Day.

Obama visited Hiroshima on Friday, becoming the first sitting American president to do so since the 1945 bombing despite concern it could dilute Japan's wartime aggression by making the country look more like a victim, rather than the one who started the Pacific War by bombing Pearl Harbor.

Just days ahead of the visit, Japan's Foreign Minister Fumio Kishida sought to reinforce the notion of victimhood, saying the atomic bombings of Hiroshima and Nagasaki were "extremely regrettable" and do not conform to "humanitarianism."

The visit also raised eyebrows of many World War II veterans and their children who believe that the decision to drop the bombs saved countless American lives that would otherwise have been lost.

Sarah Palin, the 2008 Republican vice presidential nominee and now a key supporter of Trump, also denounced Obama's visit as an "apology lap," accusing him of "dissing our vets."

Speaking at a Trump campaign rally in San Diego on Friday, Palin said the visit amounts to suggesting, "We were wrong to prove that we would eradicate evil in World War II."

American veterans groups had urged Obama not to visit Hiroshima until the Japanese apologize for the wartime treatment of American prisoners of war, thousands of whom died of abuse and starvation in Japanese prison camps.

But Japanese Prime Minister Shinzo Abe made clear that he has no plans to visit Pearl Harbor. Instead, Abe sought to emphasize Japan's image as a victim.

"In Hiroshima, numerous citizens sacrificed their lives, and even now there are those of us suffering because of the atomic bombing. And what those Japanese people suffering from the atomic bomb desire is never to repeat such tragedy in the world," Abe said during a joint news conference after talks with Obama.

Obama's decision to go to Hiroshima could be the latest in a series of efforts to build his legacy in his final year in office.

It could also be a reward for a nation that has done everything possible to help address American economic and security needs in a region marked by China's rise, including expanding Japan's military roles overseas.

White House officials have stressed that the visit wasn't an apology, and that it was aimed at highlighting his commitment to pursuing the peace and security of a world without nuclear weapons" and to honor the memory of all innocents who were lost during the war.

During Friday's visit to the Hiroshima memorial, Obama laid a wreath and delivered a long speech honoring all innocent victims of the war, including Korean victims, while underscoring his call for a world without nuclear weapons.

Obama's mention of Korean A-bomb victims, which also marked the first time for a U.S. president to do so, was seen as an effort to underscore the point that the visit was aimed at honoring all victims of the atomic bombings and does not represent an apology to Japan.

But Obama stopped short of visiting a separate memorial honoring Korean victims. (Yonhap)