Turkey's Prime Minister Recep Tayyip Erdogan on Friday came under withering criticism from Israel, Washington and the United Nations for comments branding Zionism a "crime against humanity."
The storm surrounding the comments is likely to dominate Friday's visit to Ankara by the new US Secretary of State John Kerry, who is due to hold talks there on the Syrian crisis.
Erdogan has often attacked Israeli policies in blistering language over the past several years, sending relations between the once close allies into a free-fall.
On Thursday, he told a forum organised by the UN in Vienna that "As is the case for Zionism, anti-Semitism and fascism, it is inevitable that Islamophobia be considered a crime against humanity."
Israeli Prime Minister Benjamin Netanyahu branded the comments as "a dark and mendacious statement the likes of which we thought had passed from the world."
Israel's main ally Washington said the "characterisation of Zionism as a crime against humanity... is offensive and wrong."
"We encourage people of all faiths, cultures, and ideas to denounce hateful actions and to overcome the differences of our times," said National Security Council spokesman Tommy Vietor.
A spokesperson for UN chief Ban Ki-moon, who was present when Erdogan made the inflamatory remarks at the Fifth Global Forum of the Alliance of Civilizations, also condemned the statements.
"The Secretary-General believes is it is unfortunate that such hurtful and divisive comments were uttered at a meeting being held under the theme of responsible leadership," Ban's office said in a statement.
"The Secretary-General heard the Prime Minister’s speech through an interpreter," it said.
"If the comment about Zionism was interpreted correctly, then it was not only wrong but contradicts the very principles on which the Alliance of Civilizations is based.