BANGKOK » Thailand’s premier university has apologized for displaying a billboard that showed Adolf Hitler alongside Superman and other superheroes, saying Monday (Sunday on Hawaii) it was painted by ignorant students who didn’t realize Hitler’s image would offend anyone.

The huge billboard was placed outside the art faculty of Chulalongkorn University as part of a tribute to this year’s graduating class.

It said "Congratulations" in bold white letters and showed Hitler with his arm raised in a Nazi salute next to Batman, Captain America, the Incredible Hulk and Iron Man.

"(We) would like to formally express our sincere apology for our students’ ‘Superhero’ mural," art school dean Suppakorn Disatapundhu said in a statement issued Monday. "I can assure you we are taking this matter very seriously."

The billboard was up for two days before being removed Saturday in response to criticism. Online photographs showed graduating students in their robes, mimicking Hitler’s raised arm salute.

Suppakorn said that freshman art students had painted the banner as part of a traditional send-off from incoming students to the graduating class, and it was one of dozens of banners and billboards across the campus during the university’s commencement period.

The artistic vision behind the picture was to show that good and bad people co-exist in the world, Suppakorn said after summoning the students for an explanation.

"They told me the concept was to paint a picture of superheroes who protect the world," the dean said in a telephone interview.

"Hitler was supposed to serve as a conceptual paradox to the superheroes," he said, noting that the superheroes were painted in vivid colors, while Hitler’s image was in grey scale. "This kind of thoughtless display will not happen again."

The Simon Wiesenthal Center, an international Jewish human rights group, had criticized the banner prior to its removal.

"Hitler as a superhero? Is he an appropriate role model for Thailand’s younger generation — a genocidal hate monger who mass murdered Jews and Gypsies and who considered people of color as racially inferior," Rabbi Abraham Cooper, associate dean at the center, said in a statement Friday. "The Simon Wiesenthal Center is outraged and disgusted by this public display at Thailand’s leading school of higher education."

The study of history in the Thai school system revolves primarily around the history of Thailand and its long line of kings. World history is glossed over, with little or no mention of the Holocaust.

Associated Press writer Thanyarat Doksone contributed to this report.