Read the Pope's speech to be read in absentia at La Sapienza (Italian)

In a volte face by the Vatican a controversial visit to Rome's ancient La Sapienza University by Pope Benedict XVI on Thursday was today called off apparently because of security concerns amid mounting protests by both students and academic staff.

The Vatican, which had earlier insisted the visit would go ahead, said it was "opportune to postpone".

A hundred militant left wing students had occupied the office of Professor Renato Guarini, the university rector, to demand that the papal visit be cancelled because of Benedict's "obscurantist" stand on science in general and the Church's treatment of Galileo as a heretic in particular. Sixty-seven science professors and lecturers at La Sapienza signed a letter to Professor Guarini calling on him to scrap the visit. Professor Guarini said the Pope was "saddened" by the protests.

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Students had said they would greet the Pope with a "sonic siege" of loud rock music - which he once defined as "the devil's work" - an "anti clerical" gay and lesbian parade and banners reading "No Pope" and "Knowledge needs neither fathers no priests".

The Pope, who had been invited by Professor Guarini to inaugurate the academic year, was to speak to 1,000 hand-picked guests in the Aula Magna, the main lecture hall.

The Vatican announcement was greeted with applause by protesting students at the university campus. However Romano Prodi, the Prime Minister, said he deeply regretted the cancellation and condemned the "declarations and behaviour which have provoked unacceptable tensions and created a climate which does no honour to Italy's traditions of civilisation and tolerance." He expressed "solidarity" with the pontiff, saying "No voice should be silenced in our country, least of all that of the Pope".

Sergio Doplicher, a mathematics lecturer, said "I have no objection to the Pope coming to give us his blessing but have serious reservations about him restating the supremacy of faith over science and of moral principles over the lay values protected by the Italian Constitution".

Behind the controversy over faith and science lies a broader row over what many see as the Vatican's interference in Italian affairs on issues such as stem cell research, abortion and same sex civil unions. The Pope was to speak on the death penalty and the wider theme of the Church's "defence of life".

The La Sapienza student website said Pope Benedict had "condemned centuries of scientific and cultural growth by affirming anachronistic dogmas such as Creationism while attacking scientific free thought and promoting mandatory heterosexuality".

Professor Guarini agreed that science was a "lay" discipline, but said by definition a university was "open to all as a forum for ideas". He said the protests were by a "very small part of the academic community", adding "Despite differences in opinion, Benedict XVI should be welcomed as a man of great culture and profound philosophical thought, a messenger of peace and those ethical value that we all share".

Francesco Rutelli, the deputy Prime Minister and a former mayor of Rome, said "the people who want to prevent Pope Benedict from speaking have a strange idea of liberty. The idea of silencing him in a forum for study, learning and dialogue is inconceivable." He noted that La Sapienza had been founded by Pope Boniface VIII in 1303, and said Pope Benedict was a distinguished thinker, theologian and former university teacher in his native Germany.