Vatican City - Pope Benedict XVI on Friday warned against "the impending danger" of a clash of civilizations and reaffirmed the importance of the celibacy rule for priests as he prepared to lead Christmas celebrations in Rome's Basilica of St Peter. "The year that draws to a close," the pope said, will be remembered for "the horrors of the war that took place in the Holy Land and the general danger of a clash of civilizations and religions - an impending danger that still threatens our times," Benedict said in an address to the Roman Curia - the Church's central administration.
The pope also looked back on his four trips abroad, paying tribute to his predecessor, Pope John Paul II, while reaffirming the importance of the traditional family and his opposition to same-sex unions.
Referring to the Church's strict rules on priestly celibacy, which some would like to relax, Benedict said celibacy was "a testimony of faith" that was more necessary than ever.
Echoing his famous September 12 speech in Regensburg, Germany, Benedict also called for increased dialogue between faith and reason.
"The power of Man, which has increased thanks to science, is becoming a danger that threatens Man itself and the world," Benedict said.
The 79-year-old pontiff also recalled his recent trip to Turkey and reaffirmed his respect for Islam.
He said the Islamic world was today facing a challenge "very similar to the one imposed on Christians by the Enlightenment".
"On the one hand, one should oppose the dictatorship of positive relativism, which excludes God ... On the other, it is necessary to welcome the real achievements of the Enlightenment, human rights and especially religious freedom," he said.
Benedict said dialogue between Christians and Muslims should involve finding the right solutions to such challenges and offered his solidarity to Muslims "who commit themselves against violence and in favour of synergies between faith and reason, between religion and freedom."
He also spoke out on Friday against legal recognition for unmarried couples and "dismal theories" on the rights of gays to marry which he said stripped men and women of their innate sexual identity.
"I cannot hide my concern about legislation on de facto couples," the Pope said in a Christmas address to the Rome clergy, weighing into a raging debate in Italy over what legal rights should be given to unmarried and gay couples.
Tensions have been rising in recent months between the Vatican and left-wing parties in Prime Minister Romano Prodi's ruling coalition, which has pledged to grant some kind of legal recognition to unmarried couples.
Some centre-left politicians have scorned the Vatican for speaking out against the initiative, but the Pope said the Church had the right to be heard.
"If they say the Church shouldn't interfere in these matters, then we can only reply: should mankind perhaps not interest us?" he said.
The Pope said granting legal recognition to unwed couples was a threat to traditional marriage, which required a higher level of commitment.
But he saved his strongest words for those who suggest gay couples should be put on the same level as a husband and wife.
"This tacitly accredits those dismal theories that strip all relevance from the masculinity and femininity of the human being as though it were a purely biological issue," the Pope said.
Theories "according to which man should be able to decide autonomously what he is and what he isn't," end up with mankind destroying its own identity, he said.
Two parliamentarians in the ruling coalition this week outraged fellow lawmakers by placing four dolls representing homosexual couples near the baby Jesus in the official nativity scene in Italy's parliament.
They said their gesture was to promote legal recognition for unmarried couples and the legalisation of gay marriage.
The pope was expected to lead a midnight Mass in St Peter's on Sunday and impart his traditional Christmas Day and Urbi et Orbi blessings on Monday.