Italy joined most of its European partners in abstaining on a vote which criticizes the Jewish state for restricting access to the Al-Aqsa mosque compound in a way that Israel says denies Judaism's connection to the city.
“It is incomprehensible and unacceptable, it was a mistake,” Renzi told Italian radio.
The premier said he had issued instructions to Italian diplomats to take a different stance if the same issue arises again in international bodies.
“Suggesting that Jerusalem and Judaism have no connection is like suggesting the sun causes darkness,” he said. “If we have to break with European unity on the subject, so be it.”
The executive board of UNESCO, the UN's cultural, scientific and educational arm, backed the controversial resolution on “occupied Palestine” on Tuesday.
Referring throughout to “the occupying power,” it condemns Israel for restricting Muslims' access to the Al-Aqsa mosque compound – Islam's third holiest site – and criticizes damage by security forces to the site and nearby excavations.
Israel is furious that the resolution refers to the Jerusalem Old City site only by its Muslim name, Al-Aqsa or Al-Haram al-Sharif.
It is considered holy by Muslims, Christians and Jews. Jews refer to it as the Temple Mount and it is considered the holiest site in Judaism.
Israel occupied east Jerusalem and the West Bank in 1967 in a move never recognized by the international community.