Flanked by Ecumenical Patriarch Bartholomew I after mass at the patriarchal Church of St. George, the pontiff complained in a speech that "the process of secularization has weakened the hold of ... (Christian) tradition" in Europe.

"In the face of this reality, we are called, together with all other Christian communities, to renew Europe's awareness of its Christian roots, traditions and values, giving them new vitality," he said.

His statement came just two days after he reportedly told Turkey's Islamist-turned-conservative Prime Minister Recep Tayyip Erdogan, in what was widely seen as a spectacular U-turn, that he supported Turkey's membership in the European Union.

Turkey in the EU, he had said while still Joseph Cardinal Ratzinger, would be "a grave error... against the tide of history."

Religious freedom

In a later joint declaration with Bartholomew I, at the risk of once again rubbing up his hosts the wrong way, the pontiff said respect for religious freedom must be a criterion for membership in the EU, which must ensure that its members respect the rights of their religious minorities.

It was near-overt backing for the patriarchate's complaints of restrictions imposed on it by Turkey, including the closure of a theological seminary and the confiscation of a number of properties from Christian foundations.

Another bone of contention is Turkey's refusal to recognize Bartholomew I as the ecumenical, or universal, leader of about 150 million Orthodox faithful around the world.

Turkey repeated on Thursday it has no intention of budging on this issue.

"We see the patriarchate as a Turkish institution and this is how our laws, too, see it," said foreign ministry spokesman Namik Tan. "Other definitions are in no way binding for us. We have proclaimed to the world that we do not recognize the title 'ecumenical.'"

Overcoming the schism

Benedict XVI and Bartholomew I have both put reconciliation of the Catholic and Orthodox Churches high on their agendas, and the pope described the schism, which dates back to 1054, as a "scandal to the world."

But he remained steadfast on a key point of contention between the two rites -- papal authority -- by referring in his speech to the Catholic leader's "universal responsibility."

Gestures of reconciliation

On Thursday evening, Benedict XVI became the second pope in history to set foot in a mosque -- after John Paul II in Damascus in 2001 -- when he visited Istanbul's famed Blue Mosque, coming from the nearby 6th century basilica-museum of Hagia Sophia.

The Hagia Sophia visit has angered Muslim hardliners, who perceive the visit as proof of an effort to reclaim the building -- a mosque under Ottoman rule before becoming a museum under the republic -- as a church.

But during his visit to the Blue Mosque, the pope turned towards Mecca in a gesture of Muslim prayer, his hands crossed over his stomach, at the suggestion of the Muslim cleric accompanying him. He remained for several seconds with his eyes closed.

The pope returns to Rome on Friday.