The Italian clothes company, Benetton, launched a campaign called 'Unhate' in which leaders from opposite sides of the political and religious divide appear to exchange kisses.
One of the pictures, which will be used on billboards, in Benetton shops and on websites worldwide, showed Benedict XVI kissing Ahmed el Tayyeb, an Egyptian imam and a prominent figure in Sunni Islam.
"This shows a grave lack of respect for the Pope, an offence to the feelings of believers, a clear demonstration of how publicity can violate the basic rules of respect for people," said Father Federico Lombardi, the Vatican's spokesman.
He said the Holy See was considering taking legal action against the fashion company.
The image, which is guaranteed to offend Catholics around the world, briefly appeared on a banner which was draped over the side of a Renaissance stone bridge near the Vatican, in the centre of Rome.
Hanging the banner was part of a series of "guerilla actions", the company said, which included the unveiling in Paris of an image of Nicholas Sarkozy smooching Angela Merkel and the unfurling of a banner outside Milan Cathedral depicting Barack Obama kissing his Chinese counterpart, Hu Jintao.
"Is it not possible that Benetton could have come up with anything better?" said Luca Borgomeo, the head of the Association of Italian Catholic Television Viewers.
The provocative advertising campaign also included digitally-manipulated images of Benjamin Netanyahu, Israel's prime minister, locked in an embrace with Mahmoud Abbas, the Palestinian leader.
Alessandro Benetton, the deputy head of the company, acknowledged that the advertisements were provocative but said the campaign was designed to give publicity to "an ideal notion of tolerance."
"The central theme is the kiss, the most universal symbol of love, between world political and religious leaders," he said in a statement.
Benetton has become well known for its controversial publicity campaigns, which in the past have included the image of a nun kissing a priest and parents grieving over a man dying of Aids.