Vandals spray-painted anti-Zionist graffiti at Israel's Yad Vashem Holocaust memorial, its chairman said Monday, suggesting radical ultra-Orthodox Jews were to blame.

Yad Vashem Chairman Avner Shalev told Army Radio that anti-Zionist graffiti was painted at 10 spots across the memorial compound, including a slogan that read, "Hitler, thank you for the Holocaust," and, "Jews, wake up, the evil Zionist regime doesn't protect us, it jeopardizes us."

"It's a very grave crossing of a red line," Shalev said. Asked if he suspected radical ultra-Orthodox Jews were to blame, he said the slogans were written in excellent Hebrew handwriting and one was signed "world ultra-Orthodox Jewry."

Many Ultra-Orthodox Jews are anti-Zionist because they think a Jewish state should not be established before the coming of the Messiah. Some subscribe to the conspiracy theory that Israel's founders colluded with Hitler to achieve their goal of establishing a state for Jews.

Police spokesman Micky Rosenfeld said the case was under investigation but no suspects had been identified.