Prime Minister Benjamin Netanyahu responded last Thursday for the first time to comments by Turkish Prime Minister Recep Tayyip Erdogan, who called Zionism a "crime against humanity."

"I strongly condemn the comparison that the Turkish prime minister drew between Zionism and fascism," Netanyahu said. "I had thought that such dark and libelous comments were a thing of the past."

Speaking Wednesday in Vienna at the opening session of the fifth United Nations Alliance of Civilizations, Erdogan argued that the UN and European Union are not doing enough to fight hatred of Muslims and intolerance of other cultures. But Zionism was mentioned in passing.

Just like Zionism, anti-Semitism and fascism, it becomes unavoidable that Islamophobia must be regarded as a crime against humanity,” Erdogan said in his speech. UN Secretary-General Ban Ki-moon, UN General Assembly President and former Serbian Foreign Minister Vuk Jeremic and several high-ranking Austrian officials sat near him on the stage while he spoke.

The UN itself is often accused of being anti-Israel. In November 1975, the UN General Assembly passed a resolution saying Zionism was “a form of racism and racial discrimination.” The resolution was put forward by the Soviet Union and Arab states and passed by a large majority. Only in 1991, after the fall of the Soviet Union, did the body pass another resolution repealing the anti-Israel one.

The United States, Germany, the United Kingdom and other countries have been trying for months to mediate the diplomatic crisis between Israel and Turkey, which began when Israeli soldiers boarded a ship headed for the Gaza Strip and killed nine Turkish activists. The Turkish government demands Israel apologize for the deaths, pay compensation to the families of the deceased and lift its naval blockade of Gaza.

Several days ago, German Chancellor Angela Merkel visited Ankara and spoke with Erdogan about reconciliation with Israel, among other subjects. U.S. Secretary of State John Kerry will arrive in Ankara on March 1, where he is also expected to broach the subject with the Turkish premier. It is not clear whether he will mention Erdogan’s harsh anti-Israel statements.

Israel and Turkey held halting talks to repair their relations over the past three years, but have failed to reach an agreement. Defense Minister Ehud Barak and National Security Adviser Yaakov Amidror have pressured Prime Minister Benjamin Netanyahu to apologize to the Turks and end the crisis. But Netanyahu is reluctant to do so because of the likely political ramifications. His political ally, former Foreign Minister Avigdor Lieberman, strongly opposes such a move.