Vatican: Pope Benedict sets off today on one of the most delicate trips by a Pontiff, visiting Turkey, where resentment is seething over his comments on Islam and opposition to Ankara's EU bid.

The visit by the leader of 1.1 billion Roman Catholics was originally intended to be a Christian event centred around a meeting with the Istanbul-based head of the world's 250 million Orthodox Christians.

But it has taken on much vaster political ramifications in Western-Islamic relations, East-West ties, Catholic-Muslim relations and Turkey's own aspirations to be part of Europe.

The 79-year-old pope will have to attempt to repair damage on several fronts as he visits the predominantly Muslim country that is officially secular.

The attitude to the pope in Turkey ranges from total secular indifference to passionate religious or political anger.

Benedict infuriated Muslims worldwide in September with a lecture that appeared to portray Islam as a religion tainted by violence. He later expressed regret over the pain his remarks caused but stopped short of a full apology.

Many Islamic officials want him to state clearly that he believes Islam to be a religion of peace.

"I think the attitude the pope should take is that neither Islam nor Christianity is a source of violence," said Ali Bardakoglu, who heads Ankara's Directorate General for Religious Affairs.

In a post-September 11 world, Benedict is expected to strongly re-state his belief that all religious leaders should take a united stand that religion can never be used to justify violence.

One possible gesture of reconciliation will come on Thursday, when the Pope will make a hastily added visit to Istanbul's famous Blue Mosque.

It will be his first visit to a mosque as pope and only the second ever by a pontiff. His predecessor John Paul II became the first pope to visit a mosque, in Damascus in 2001.

Turkey plans tight security measures for the pope, whose trip takes in the capital Ankara, the commercial and cultural hub of Istanbul, where tens of thousands of people took part in a "Pope, don't come" demonstration on Sunday.