Al-Azhar, whose grand imam was pictured kissing the pope in a photo montage by Italian clothes company Benetton, on Thursday slammed the advertisement as "irresponsible and absurd."
So absurd was the concept that the institution -- Sunni Islam's highest seat of learning -- "is still hesitating as to whether it should issue a response," Mahmud Azab, adviser to Grand Imam Ahmed el-Tayyeb, told AFP.
Azab said he wondered if this type of campaign was "in fact dangerous for universal values and freedom of expression as understood in Europe."
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For its part, the Vatican said Thursday it was taking legal action against Benetton, despite the Italian clothing company agreeing on Wednesday to pull the photo, saying it was "sorry that the use of the image had so hurt the sensibilities of the faithful."
Benetton's poster showed Pope Benedict XVI kissing on the lips Egypt's Ahmed el-Tayyeb, a leading voice in Sunni Islam.
It launched Wednesday a new global advertising campaign called UNHATE that contained a series of photo montages of political and religious leaders kissing.
The company had defended the campaign, saying its purpose "was solely to battle the culture of hate in all its forms".