"Hitler, thank you for the wonderful Holocaust" was one of the slogans spray painted overnight Sunday on the open campus of Yad Vashem, Israel's main Holocaust memorial site.

The graffiti mainly targeted Zionism, with slogans like "Jews, wake up, the evil Zionist regime is not protecting us, it is only putting us in harm's way," and "If Hitler didn't exist, the Zionists would have invented him" led police to believe that the perpetrators of the shocking vandalism were members of a radical ultra-Orthodox sect well known for its anti-Zionist views. Other avenues, however, are also being investigated.

Seven giant slogans — including one that read: "Thank you Hitler for your wonderful Holocaust that you arranged for us, it's only because of you that we got a state at the UN" — were sprayed in Warsaw Ghetto Square near the sculpture depicting the Warsaw Ghetto uprising.

Another slogan read: "To the respectable government of Poland, stop allowing the Zionists to conduct manipulative commemorations at Auschwitz."

The message was signed "World Haredi Judaism."

Another said: "The war of the Zionist regime is not the war of the Jewish people," fueling suspicion that a small fringe of ultra-Orthodox Jews, who are virulently opposed to the state of Israel, were to blame, AFP reported.

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.

The red, white and black graffiti was written in both formal Hebrew characters as well as in handwritten script.

"We are shocked and confused by this callous expression of burning hatred against the Zionists and Zionism,” said Yad Vashem Chairman Avner Shalev. “This unprecedented act crosses a red line. I have reported it to Education Minister Gideon Sa’ar, who also expressed his bewilderment. I also spoke to Yad Vashem Council Chairman Rabbi Israel Meir Lau, who joined me in expressing his concern over this grave deed."

Shalev reported that the graffiti was written in very good Hebrew, very likely by more than one person. "The texts refer to the collusion between Zionism and Hitler and one of them is signed by 'World Haredi Judaism'," he said.

He added that there had been no prior warnings but insisted that the incident did not indicate a security problem.

Israeli ministers condemned the act of vandalism on Monday, with Public Diplomacy and Diaspora Affairs Minister Yuli Edelstein, who oversees the prevention of anti-Semitic offenses, saying "this is an escalation and an unprecedented crossing of lines."

"To spray paint graffiti on a memorial for millions of victims is to spit in the face of the State of Israel and in the face of the dead and to defile their memory," Edelstein added. "I am convinced that the Israel Police will apprehend the culprits quickly, and I call upon the authorities to prosecute them to the fullest extent of the law."

Sa'ar also commented on the incident, saying that "those who defiled and corrupted Yad Vashem with these deranged slogans did it with the express intention of insulting the public."

Public Security Minister Yitzhak Aharonvitch instructed the police to investigate the incident and to "rapidly apprehend these disgusting criminals who targeted one of Israel's most prominent symbols."

The Jerusalem municipality had cleaned the graffiti off the walls by Monday afternoon.