LEETSDALE, Pa. -- A Pennsylvania school district has apologized after quotes from Adolf Hitler, Joseph Stalin and the leader of the Islamic State of Iraq and Syria, or ISIS, were printed in the graduating class section of this year's high school yearbook.

"Though the content of the quotes was reviewed thoroughly, the attributions clearly were not," Quaker Valley School District officials said in a statement Wednesday. The Pittsburgh Tribune-Review first reported the situation.

The Hitler quote is "Words build bridges into unexplored regions." Stalin's statement is more menacing: "Ideas are more powerful than guns. We would not let our enemies have guns, so why would we let them have ideas?"

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The third quote is from Abu Bakr al-Baghdadi: "Be just: the unjust never prosper. Be valiant. Keep your word, even to your enemies."

Students can get a refund on the books, or stickers to cover up the quotes.

The yearbooks cost at least $69, but can go for more than $100 if students have their names engraved, district spokeswoman Angela Yingling said.

Students submit quotes from famous people for inclusion in the yearbook, but Yingling said, "publishing the quotes is a shared responsibility of the yearbook staff, sponsor and administration."

The district won't say if students or anyone else faces punishment for the quotes.

Senior Dominique Cagliuso said she plans to cover the quotes in her book with the school-issued stickers.

"It makes the entire senior class look badly," she said. "It's also confusing how nobody caught it before it went out. It's one thing to have a silly quote from your favorite TV show, but to have a quote from dictators is disrespectful."

Quaker Valley High School has more than 630 students in grades 9-12, and Yingling said more than 360 of the yearbooks were distributed.

School board president Sarah Heres said she's "confident steps will be taken to ensure this lack of oversight does not happen again."

"This is a regrettable mistake, as the school district would never knowingly condone this messaging in a school-sponsored publication," the district said in a statement. "We are well aware of the emotions this has conjured in many of our students and their families, and for that we are sorry."