BANGKOK (AP) — Thailand's premier university has apologized for displaying a banner that showed Adolf Hitler alongside Superman and other superheroes. School officials say it was painted by ignorant students who didn't realize Hitler's image would offend anyone.

The huge banner said "Congratulations." It was hung outside the art school of Chulalongkorn University for this year's graduating class.

Art school Dean Suppakorn Disatapundhu said Monday that freshman students had painted the banner. He called their mistake "the result of pure ignorance."

In a statement, the dean issued a "sincere apology" from the university.

The banner was up for two days and taken down Saturday in response to criticism.

Online photographs showed graduating students in their robes, mimicking the image of Hitler with one arm raised in the Nazi salute.