ANKARA, Turkey — Turkish Prime Minister Tayyip Erdogan's comment equating Zionism with crimes against humanity is "particularly offensive" and has a "corrosive effect" on U.S.-Turkish relations, a senior U.S. official said on Friday.

"This was particularly offensive, frankly, to call Zionism a crime against humanity," the senior U.S. official told reporters as Secretary of State John Kerry flew to Ankara. "It does have a corrosive effect [on relations]."

"I am sure the secretary will be very clear about how dismayed we were to hear it," the official, who spoke on condition of anonymity, added.

Erdogan told a U.N. Alliance of Civilizations meeting in Vienna on Wednesday: "Just as with Zionism, anti-Semitism and fascism, it has become necessary to view Islamophobia as a crime against humanity."

The comments, condemned by the head of Europe's main rabbinical group as a "hateful attack" on Jews, are likely to hit efforts to rebuild ties with the Jewish state, undermining a role Washington had hoped Turkey, once Israel's only Muslim ally, could play as a broker in the Middle East.

"Not that long ago [you] had these two countries demonstrating that a majority Muslim country could have very positive and strong relations with the Jewish state and that was a sign for the region [of what was] possible," the U.S. official said.