Pope Francis and the spiritual leader of the world's Orthodox Christians have called for peace in Ukraine and appealed to all sides to pursue dialogue based on international law to resolve the conflict.
Francis and Ecumenical Patriarch Bartholomew I issued a joint declaration on November 30 in Istanbul at the end of a lengthy liturgy to mark the feast of St. Andrew, an important feast in the Orthodox Church.
In the statement, the two Christian leaders said they were praying for peace in Ukraine "while we call upon all parties involved to pursue the path of dialogue and of respect for international law in order to bring an end to the conflict and allow all Ukrainians to live in harmony."
The celebration was the main reason for Francis's three-day visit to Turkey.
Despite his position, Bartholomew has little real sway over the Russian Orthodox Church, which has the largest flock in the faith and has tense, politically charged relations with rival churches in Ukraine.
Francis and Bartholomew also demanded an end to the violent persecution of Christians in Syria and Iraq by Islamic State (IS) jihadists.
The two church leaders also called for "a constructive dialogue with Islam based on mutual respect and friendship."
The visit by Pope Francis, the leader of the world's 1.2 billion Catholics, is seen as a crucial test of his ability to build bridges between faiths amid the rampage by IS jihadists in Iraq and Syria and concerns over the persecution of Christian minorities in the Middle East.
Pope Francis and Patriarch Bartholomew I presided over an ecumenical prayer service at the Orthodox patriarchate on November 29.
The Ecumenical Patriarchate of Constantinople is one of 14 autocephalous (self-led) churches that make up Orthodox Christianity, and Bartholomew frequently acts as an intermediary between Orthodox and other Christian believers, including Catholics and Protestants.
The patriarchate is considered the "first among equals" among the 14 Orthodox churches because of its historical location in what was the capital of the former Eastern Roman Empire, or Byzantium.
However, it does not exercise control over the other individual churches and is dwarfed in size by the Russian Orthodox Church, the largest Orthodox congregation in the world.
During his November 29 visit to Sultan Ahmet mosque, popularly known as the Blue Mosque, the pontiff closed his eyes and engaged in a moment of apparent reflection as he stood alongside the grand mufti of Istanbul, Rahmi Yaram, who performed an Islamic prayer.
He later visited Hagia Sophia, which in the course of some 15 centuries of history has served as a church, a mosque, and now a museum.
The pontiff also celebrated mass in the Catholic Cathedral of the Holy Spirit, in front of a congregation that included Christian refugees from Iraq.
Iraq's Christian population has fallen by nearly 70 percent since the start of its 2003 war. Syria's total Christian minority made up around 10 percent of the population of 22 million before its civil war began in 2011.
Turkey's own Christian community is tiny -- just 80,000 in a country of some 75 million Muslims -- but extremely mixed, consisting of Armenians, Greek Orthodox, Franco-Levantines, Syriac Orthodox, and Chaldeans.
Of these only the small Franco-Levantine and Chaldean communities regard the pope as the head of their churches.
In Ankara on November 28, the pope met with Turkish leaders and called for religious tolerance and peace in the Middle East.
After meeting Turkey's top cleric Mehmet Gormez in Ankara, Francis called the situation in Iraq and Syria "particularly tragic."
The pope also deplored the fact that communities are being targeted simply because of their beliefs.
He also said that "fanaticism and fundamentalism, as well as irrational fears which foster misunderstanding and discrimination, need to be countered by the solidarity of all believers" and that it is "essential that all citizens, Muslim, Jewish, and Christian…enjoy the same rights and respect."